The screw holes will be all in the wrong places on any Squier, relative to a Fender Mex or USA. Fill and redrill is your only recourse (and possibly some judicious alterations around the neck pocket/pickup holes of the pickguard) if you want to fit the one you bought. Not much you can do if it doesn't quite cover the control cavity though.
I managed to fit a Mex pickguard to a Squier body, but had to fill most of the existing screwholes and drill new ones, and there was a position where the control cavity would be filled (just), but it left a small gap at the heel of the neck.
The alternative would be to get a copy made of the existing Squier one, there are a few places which will copy a pickguard for you. That at least ought to be a reasonable match.