...I haven't EVER been succesful with trimming mid-air. I am new in the trimming stuff...
Trimming, while flying, is a skill you
must learn. It's easy once you know how. All planes that are out of trim are difficult to fly.
Think about what stick inputs you are giving it to make it fly straight. Then move the trim tabs the same direction.
Example: If the plane climbs, you will need to input down elevator (push forward on the elevator) to make it fly straight. To trim the elevator, push forward on the trim tab. Keep adding elevator trim until the plane no longer climds. All of the other axis are the same, what ever direction you push the stick to correct, push the trim tabs that same direction until the plane flies straight.
Every plane I have ever owned has needed some trim. I trim some of my planes every time I fly them, not by much, but still a click or two.