That "going out of control" thing you mentioned is called a spin. Your wing is way too small to carry the plane's weight, and your elevator control is too hot. So every time your pilot pulls back on the stick he tip stalls a wing, which puts the plane into a spin. Calculate your wing loading. A good flying RC model at this size will be between 15-20 ounces per square inch. I'll bet you had 35 ounces per square inch with that tiny wing.

You said you have a bigger wing? You need to size the tail to the wing, so if you are changing the wing size much you'll need to build a new tail too.