Ouch, dont start filing stuff on a brand new gun ! If the mags dont pop out, there is something wrong with the gun, not the mags. I just double-checked on mine and both the 7 (that lives in the gun) and 9 (that lives in the mag pouch) fall free if I push the mag release.
I didn't touch the gun, only the mag slots on one 9-round mag. I'd love to know what makes the higher round-count mags so hard to drop...but I don't think it's the gun.