if the ailerons are in a slight spoileron position it may be possible that they may be effecting your hover. Try to get the ailerons flat to the wing and move your CG back.....some planes hover with some up elevator anyway depending on how it is designed......if i was you i would go out on a calm day and try to get it in the complete vitical postion and see what happens......is it possible that there is some wind blowing your plane around?

Good Luck!!