Scheduled Shutdown with cancel option

HI - I've been asked to deploy a script that runs once a week on a Friday evening, that shuts down any PCs left on by users in the office BUT it must warn them its happening and allow them to cancel if they are still working.

I thought this would be trivial but it appears not. The issue i have had is that any script i've tested (even when run as logged in user) seems to ignore my pop up prompts to allow cancel and just schedules the shutdown? Ive shoved an example vbscript script i was testing below but open to any alternatives if someone can assist?

There seem to be paid for solutions for this, but i cant believe it cant simply script this, rather than was 1k for someone else's code?!

--------shutdown.vbs----------

Option Explicit
Dim objShell, intShutdown
Dim strShutdown, strAbort

' -s = shutdown, -t 120 = 2 minutes, -f = force programs to close
strShutdown = "shutdown.exe -s -t 300 -f"
set objShell = CreateObject("WScript.Shell")
objShell.Run strShutdown, 0, false

'go to sleep so message box appears on top
WScript.Sleep 100

' Input Box to abort shutdown
intShutdown = (MsgBox("Your Computer will shutdown in 5 minutes. Do you want to cancel computer shutdown and continue working? If so then click the YES button. Please don't forget to shutdown when you have finished",vbYesNo+vbExclamation+vbApplicationModal,"Cancel Shutdown"))
If intShutdown = vbYes Then
' Abort Shutdown
strAbort = "shutdown.exe -a"
set objShell = CreateObject("WScript.Shell")
objShell.Run strAbort, 0, false
End if

Wscript.Quit