Robert, the Magpul Polymer Magazines are slightly over thick to compensate for structural integrity Sir. I use metal magazines which work without issue. You can try using colored chalk, orange or yellow. insert the magazine, remove and try dremel/sanding down the areas of contact (largest scuff marks, for a better fit. Just do it gradually and repeat until better fit. Cheers and stay safe!

I've now been waiting for exactly 2 weeks for my background check to go through so I can get my Zastava Zpap M70 from my FFL there's apparently a huge backlog of background requests here in Oregon, I bought a couple different Magazines, I bought 2 pmags, 1 with steel lug, 1 Polymer, 1 Bulgarian surplus mag, and one palm USA mag (with steel reinforcement) id just run it a bit Polymer can flex and it will likely get a little smoother after you've put some rounds through it, but seeing as I don't have mine yet I can't say for sure if this is normal.
The Surplus mags are inexpensive, and readily available all over the place, so if the magpul one doesn't smooth out look into the metal mags.