Help please

I brought a MDL-A3-BSX-Un-Z100 from Marchant Dice a year ago and have only done a little with it.
So I have not explored all of its potential just done a little engraving and that’s it.
So I come to start to do some more crafty things with it and it does not do what it is told?
So I think I know I will do a square…….big mistake …….
I set it up to do a simple square with straight corners and I got round corners?
So I ran it again and watched the mach3 window
I could see the tool path and then I could see the path it had taken …mmmmm very different?
So I contacted them and sent them the tool paths and they said that they are good.
They suggested to me that I check all couplings which I have done and all seem good.
I also did a few other tests and doing a simple O it comes out good.
So it looks like when it comes to change direction from a straight line I get the issue.

I’m using Vectric VCarve Pro 7 and Mach3

So please does anyone have any ideas.

Cheers Aaron