Try firing off a few shots as you screw in your tank and keep trying to screw it in. If you're using the stock reg for the Mini, lots of times, it becomes hard to screw in way before it is all the way in (that's what she said). Firing a few shots should allow some pressure to be removed making it easier to screw in the tank. If not, you can always get an on/off for it making it really easy to screw in your tank, resolving your issue.
Dust Red Invert Mini | 14" DeadlyWind | Dye Rotor | 50/4500 Ninja Tank