SDL2 program running too fast despite use of time delta

Question

I'm following Games From Scratch's page here while trying to make a simple pong game in C + SDL2. I'm trying to make the ball move, but found it always moves too fast, even after following this.

Here's the code in question:

// Update ball position
prevTime = curTime;
curTime = SDL_GetTicks() - prevTime;
delta = curTime / 1000;
ball.y = (int) (ball.y - (BALL_SPD * delta));

Wondering if anyone can help me work out this issue? I'm simply trying to make the ball move slowly up to the top of the screen, but it goes way too fast, almost instantly.

Here's the full code:

#include <SDL.h>
#include <stdio.h>
#include <stdbool.h>

#define SCR_W 1280
#define SCR_H 720
#define BALL_SPD 5

int setUpWindowAndRenderer(SDL_Window **w, SDL_Renderer **r);
void setUpPaddles(SDL_Rect *player1, SDL_Rect *player2);
void setUpBoard(SDL_Rect *dash);

int main(int argc, char *args[]){
    // SDL Initialisation and creation of window and renderer
    SDL_Window *window = NULL;
    SDL_Renderer *renderer = NULL;

    if(setUpWindowAndRenderer(&window, &renderer) < 0){
        printf("setUpWindowAndRenderer() failed! Exiting...\n");
        exit(EXIT_FAILURE);
    }

    // SDL_SetRelativeMouseMode(SDL_TRUE);

    // Stores user input
    SDL_Event e;

    // Tests to see if game has been quit in main loop
    bool quit = false;

    // Set up both player paddles
    SDL_Rect player1;
    SDL_Rect player2;
    setUpPaddles(&player1, &player2);

    // Set up ball
    SDL_Rect ball;
    ball.x = SCR_W / 4;
    ball.y = SCR_H / 2;
    ball.w = 25;
    ball.h = 25;

    // Set up delta/timing
    float delta = 0, curTime = 0, prevTime = 0;

    // Mouse y-position
    int mY;

    // Central line initial rect
    SDL_Rect lineRect = {(SCR_W / 2) - 5, SCR_H, 10, 25};

    // Main game loop
    while(!quit){
        // Check user input
        while(SDL_PollEvent(&e)){
            if(e.type == SDL_QUIT){
                quit = true;
            } else if(e.type == SDL_KEYDOWN){
                switch(e.key.keysym.sym){
                    case SDLK_w:
                        // GO THE FUCK UP
                        break;
                    case SDLK_s:
                        // GO DOWN TO THE GROUND BOI
                        break;
                    default:
                        printf("Invalid key.\n");
                        break;
                }
            }
        }

        // Update Player 1 Paddle
        // Update P1 paddle to mouse y position
        SDL_GetMouseState(NULL, &mY);
        player1.y = mY - (player1.h / 2);

        // Limit position if paddle y pos goes below zero or above window height
        if(player1.y < 0){
            player1.y = 0;
        }
        if(player1.y + player1.h > SCR_H){
            player1.y = SCR_H - player1.h;
        }

        // Update ball position
        prevTime = curTime;
        curTime = SDL_GetTicks() - prevTime;
        delta = curTime / 1000;
        ball.y = (int) (ball.y - (BALL_SPD * delta));

        // Limit position if ball y pos goes below zero or above window height
        if(ball.y < 0){
            ball.y = 0;
        }
        if(ball.y + ball.h > SCR_H){
            ball.y = SCR_H;
        }

        // Clear screen
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
        SDL_RenderClear(renderer);

        // Draw central line
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        while(lineRect.y <= SCR_H && lineRect.y >= 0){
            SDL_RenderFillRect(renderer, &lineRect);
            lineRect.y -= 50;
        }
        lineRect.y = SCR_H;

        // Draw paddles and ball
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderFillRect(renderer, &player1);
        SDL_RenderFillRect(renderer, &player2);
        SDL_RenderFillRect(renderer, &ball);

        SDL_RenderPresent(renderer);
    }

    SDL_Quit();
    return 0;
}

int setUpWindowAndRenderer(SDL_Window **w, SDL_Renderer **r){
    if(SDL_Init(SDL_INIT_VIDEO) < 0){
        printf("SDL_Init() failed! %s\n", SDL_GetError());
        return -1;
    }


    if((*w = SDL_CreateWindow("Pong Clone", SDL_WINDOWPOS_UNDEFINED,
        SDL_WINDOWPOS_UNDEFINED, SCR_W, SCR_H, 0)) == NULL){
        printf("SDL_CreateWindow() failed! %s\n", SDL_GetError());
        return -1;
    }


    if((*r = SDL_CreateRenderer(*w, -1, 0)) == NULL){
        printf("SDL_CreateRenderer() failed! %s\n", SDL_GetError());
        return -1;
    }

    return 0; // success
}

void setUpPaddles(SDL_Rect *player1, SDL_Rect *player2){
    // Define paddle width and height
    int pW = 30;
    int pH = 100;

    player1->x = pW * 2; // Position P1 paddle 2 paddle-widths away from screen edge
    player1->y = (SCR_H / 2) - (pH / 2); // Position Paddle in direct centre
    player1->w = pW; // Paddle Width
    player1->h = pH; // Paddle Height

    player2->x = SCR_W - (pW * 3); // Position P2 paddle 2 paddle-widths away from screen edge
    player2->y = (SCR_H / 2) - (pH / 2); // Position Paddle in direct centre
    player2->w = pW; // Paddle Width
    player2->h = pH; // Paddle Height
}