Won’t stay sighted in - Nikon P-Tactical Superdot 2 MOA Red Dot Sight

Bought with great expectations. Store I bought it from mounted it to my 20 gage and bore sighted it. Took it too my gun range and fired from 25 yards. Didn’t even hit the back board. Moved up to 10 yards and was able to get it on paper. Moved back to 25 yards and finally got it sighted in with about a 4 inch grouping. Moved out to 50 yards and it was way high and left. After multiple shots was able to get about a 5 inch grouping. First day of Deer hunting missed an easy 50 yard shot, not once but twice. Went back to gun range and found it was hitting 6-8 inches high and right. Can’t trust a sight that won’t stay sighted.