SwiftUI subview going off of the window

Question

As a SwiftUI beginner, I have just recently started creating my first MacOS app. However, when I was trying to implement the NSVisualEffectView to blur the background, the contentView that I was using went off of the screen, which wasn't visible at all. It looked something like this:

So I tried fixing the size of the text I had in the contentView by making the text I had into Text("Hello world!").frame(width: 700, height:500), and the screen became like this:

By doing this, in the bottom left corner, the tiny shapes of Hello world! can be seen. However, unless I position the text on the top right of the contentView, I can't seem to move it. Does anyone know how to fix this?

*For reference, here is the AppDelegate.swift contents:

import SwiftUI

@main
class AppDelegate: NSObject, NSApplicationDelegate {

    var window: NSWindow!


    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView()
        let visualEffect = NSVisualEffectView()
        visualEffect.blendingMode = .behindWindow
        visualEffect.state = .active
        visualEffect.material = .fullScreenUI
        visualEffect.addSubview(NSHostingView(rootView: contentView))

        // Create the window and set the content view.
        window = NSWindow(
            contentRect: .zero,
            styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
            backing: .buffered, defer: false)
        window.isReleasedWhenClosed = false
        window.center()
        window.setFrameAutosaveName("Main Window")
        window.contentView = visualEffect
        window.makeKeyAndOrderFront(nil)
        window.titlebarAppearsTransparent = true
        window.titleVisibility = .hidden
        
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }
    
}