Somewhat engine downthrust but mostly the CG is too far foward by the sounds of it.

Use a thicker than normal washer under the engine mount lugs where the rear bolts go through. Or if you've got a mount then add a wedge shim that puts the engine to 2 degrees downthrust compared to the flat bottom of the wing.

Next comes flight testing and what is called the dive test. You're going to trim the model for around mid RPM's (whatever throttle stick position that is) and trim the elevator for level flight. Then punch it over into a 60 degree dive from good height and let go of the sticks leaving the engine at the same throttle setting. Watch how the model pulls up from the dive. I'll bet it comes back to level and then noses up pretty quickly. That means it is too nose heavy and you're carrying too much elevator trim to compensate. So move the CG back about 1/2 inch and try again. As close to using the same throttle setting as you can manage but it's not really critical. Keep moving the CG back and retrimming in some down trim for hands off level and then do the dive test until the model shows that it is trying to lift the nose but it's not really doing it or it takes a LONG time to pull back to level from the dive. Avoid getting to where it just wants to straight line all the way in or where it wants to tuck to an even steeper dive. That's too far and you need to move it ahead a little.

On a large chord wing like this (the ailerons are part of the wing chord so you've got a 13.25 inch chord) moving the CG by 3/8 to 1/2 inch at a time to find the right ballpark is OK. Once you get in the range to can find tune the handling by shifting it an 1/8 to 1/4 one way or the other.

The reason it's more about the CG than the engine thrust is that if the model was dead neutral then even with the engine in line with the wing it would not nose up at all It would just accelerate. Going for a degree or two of downthrust just helps compensate for the usual amount of stability that most folks prefer. Don't try to mask the issue with downthrust. Add in a little by all means but then do the dive tests to set the CG location.

To get a head start on what you have and where your model's neutral point is (that would be the most rearward CG you should try under any circumstances) go look for the CG calculator link in the stickies in the Scratch Build forum.