Stability and speed is not set by the airfoil. It's set by the location of the balance point for the stability issue and the wing loading for the speed.

But if the paint you used on this wing has resulted in the shape deforming a lot then the differences from one side to the other will produce effects similar to warped wings or misadjusted ailerons. In some cases it'll also lead to one wing stalling before the other when trying to fly slowly so that you find that the model is extremely difficult to control.

You don't provide any details on what model it is or what paint you used or pictures. Without all that it's hard to say more about it. If it actually is the HH Extra model that is the subject of the other threads that you have then even if the wing were the right way up or properly symetrical it sounds like it's just more model than you're ready for at this point. What you need instead is another model that is more of a trainer. If you take this one back to exchange it or decide to put it on a shelf for later that's fine either way. But from your description you jumped in at too advanced a level of model for your present skill level.

Yes, the flight sims make it look easier than it is. If you based your choice on success with them then you just got bitten by the reality bug.