Try the following:

Get your plane flying up-right, straight and level using your trim settings to get it flying "hands-off".

Now do the same thing with the plane inverted. In theory you should only have to adjust the elevator trim.

The dihedral "self-leveling" stability is nothing like the forces applied by ailerons, etc. You will find that the plane "falls out" to one side of inverted, but will remoan very stable upright.

gus