You answered your own question. Too much positive incidence. Incidence is the angle of the flying surfaces relative to a neutral reference line. If you have a symmetrical airfoil laid down flat on the trailing edge, it will be too much positive. The advice to get an incidence meter is good. In fact, get two if you're going to keep scratch building. Work on the wing mount (build it up?) until the wing, tail and engine are all at 0-0-0 degrees. Test fly. You should be able to trim the plane to fly level at medium throttle, climb at full throttle, and glide gently at idle. If it climbs under power, add engine downthrust 1-3 degrees as needed. If it dives in the glide, you may need to shim the leading edge of the wing up 1-2 degrees. That ought to get you in the ballpark, assuning the balance point is about right. Try about 25% of the wing chord to start.