Well, looks like a good wing. Thanks for the web site, I see a lot there I like. Still not knowing the rest of your set up, all I can say is the following.
1) Make sure you have your c/g set at the right spot. (never mentioned if it was pitch sensitive)
2)Make sure you have the control throws set per mfg. suggestions until you learn the plane. (if your throws are more extreme then that will cause problems if not enough stick time on the plane. The Northstar is a perfect example with roll rate) Exaggerated throws can cause over correction problems and or unstable flight when input's are done.
3) If you have a computer radio, and the rates are good, you can always dial in some expo to slow the response down at and near neutral stick input's. With -expo in everything responds slower based on the % entered. You want full deflection then you just give the stick full over.

Hope this helps. I long to get another seamaster. When I am finished with a few other projects then I will get another one. I love mine and after a few mods had a really kick butt plane.