Did you mean you're using TAPE for covering? That would be bad. Only Ultracote or Icarex should be used. Anything else and who knows what will happen.

That big wing needs a lot of attention to keep it straight. Check the directions for how to trim the plane. You first need to get the roll trim even. Most likely there is a slight warp ironed into your wing. This will show up as unwanted roll trim that changes with airspeed. In that case you'll need to twist it in the opposite direction and iron it straight, one wing half at a time.

After the roll trim is good, then you can worry about washout or wash in using the same method.