Not that guy but anyways;
The ref model is straight but your prop has some sort of cave-in at the top?
Some lines that should be straight are off like the bottom of the gun.
Proportions don't match (though that's not a disaster)
Foam doesn't easily allow for the level of detail you're going for so i'd advise using some alternate materials in addition to foam for smaller details.
And desu, i'd just use screws for screws if i were you.
One thing that might help: if you want clean subtle lines running along your foam, put a ruler along your line, make a superficial cut with a very sharp knife and warm it up with a heat gun.
This will make the foam contract and leave you with clean lines.
And while we're at it, i'd just use stencils for letters and other small paint detailing if i were you.
Cutting out vinyl stickers to mask are a great way to get a crisp pattern on props too.