While I agree with the others that it sounds like it IS nose heavy you will also be fighting the flat bottom airfoil.

To TRY to compensate you can set up the controls so there is more down elevator travel than up as well as moving the balance back a bit at a time. Don't be surprised when you find you need to add down trim to compensate for the rearward CG shifting. Just keep adding down until the model is trimmed closer to neutral.

Do a search in the Sailplanes forum for "dive test". That will describe a method for sneaking up on the neutral handling CG location.

But in the end it IS still a flat bottomed trainer that you are trying to make into a stunter. I WILL NOT be happy about it and it'll constantly remind you that you're expecting too much from a model that was designed for a different mission.