Google Script Copy created the copy in my folder and not original shared folder

Question

I'm very new to scripting, and I'm having an issue with the copy function, as well as finding newer relevant information.

My end goal is to copy a google workbook in a shared folder to another shared folder with a new name.

Currently I am simply trying to copy the workbook to a new name in the same folder, but the script puts it in my folder and not the shared.

Below is the very simple script I had written. If I do the copy manually through the google sheet copy function, I can put the newly named sheet anywhere. I tried to record these steps as a macro, but that did nothing. As an FYI the Dfolder and Cfolder variables are the names of shared folders. The function is to place the copied workbook in one of these 2 folders depending upon a cell value.

function MakeCopy() {
  let Dfolder = "Defect PreTrips"
  let Cfolder = "Clean PreTrips"
  let SheetName = SpreadsheetApp.getActive();
  let Truck = SheetName.getRange("E3").getValue();
  SheetName.getRange("C3").setValue(new Date());
  Tday = SheetName.getRange("C3").getDisplayValue();
  if (Truck != "")
    {
      SheetName.copy("Pretrip " + Truck + " " + Tday);
      ClearSheet();
    }
    else 
    {
      Browser.msgBox("Truck required");      
    }
};