My first powered plane was a Midwest Aerostar 20. with a .20. It flew, but they called it the weedeater. I could barely get it into the air, and if the wind was right I had to fly between two trees and make a turn behind them to miss a third. While the urge to start with a small engine might seem good, slower and easier, the opposite is true. It is much easier to learn on an A/C that has enough power. While your plane will fly with a .20 it will take a little more skill than you have yet. I had the benefit of flying gliders for years before my first powered plane and It was still challenging to take-off and fly. I would recommend a 9-5 or 9-6 prop on a .25 sized engine and a flight instructor. If you don't want to replace the engine then I would try a 9-5 prop and instructor. Most of all I would try an instructor.