Irl, your center of mass would be way too high, but with simpleplanes physics, it's hard to judge

I can help with balance. I'll fix it tag you on an unlisted post

Can you be a little more specific? What exactly do you mean by balance? Is it tilting to one side, or is it flipping because of the engine weight in the back? If it's the engine weight in the back, I'd suggest possibly taking away the fuel from the wings, and lengthening the cone near the front and adding all fuel and dead weight in there. If it's a side to side problem, make sure you used the mirror function, it's a useful tool. If it's just too top heavy, you might need to consider removing the poles above on the wings because they could make the plane unstable. On top of that, you should add a gyroscope to make the process more smooth-lined. The gyroscope stabilizes boats and planes, so it should help, but a gyroscope by itself may not help.