"Stick Control" is something one has to develop.....and it takes practice. Small controlled movements is the key.
How do you hold the gimbal sticks.........pinch between forefinger and thumb or just thumbs?

Yes as mentioned , you have to be able to see the plane to fly it. With these smaller RTF planes you have to keep them close and that means constantly turning them left or right. If you are slamming the sticks and/or letting them spring back to center while flying you will have a very hard time trying to control the plane when it is not in SAFE mode.