This is what fixed the problem with the round corners, thanks to Scott from Mach3 here is what he sent me. I changed the settings and it worked. Thank You Scott...!
Is the square corner the one that the cut starts/stops at? That would make sense, as the other 3 corners are likely being rounded because of your CV settings. Your options are:
1). use Exact Stop (G61) instead of CV (G64) mode
2). make sure that the "Stop CV on angles >" option is enabled (Config > General Config) and set for something appropriate (60 is a good choice)
You can also control the amount of rounding by how much your CV Distance Tolerance is set for.
Thanks,
scott