Pushing the stick forward is called an outside loop. Inside is with the stick back. Sometimes I have a habit of giving a bit of ail. when doing loops without realizing it. Another thing you can try is to trim it with ails till it loops straight, then the use rudder trim to get it to fly straightand level. As said above make sure you have tha same travel on both ails. In fact you could lessen the throw on one side to make it come out level. Could be such a thing as the EPP foam twisting on one side more than the other. Lots of food for thought.