I own and shoot a USP9c, and have not experienced your alignment problem at all. Ditto for my USP40c. Check how you're gripping your gun (pressure between shooting and supporting hands, contact area of your palms and fingers, etc.)
At your next range trip, have the range officer or another shooter fire your USP9c, and see if the same results occur. If the same results happen, send your gun to HK for an inspection, and explain to them what you did. Your gun is warranty, so you're covered.