. . . . . as you go into a turn to the Left, straighten your Right Leg and "stand" on the peg - it will support your bodies weight and the centrifugal force acting on it. Your butt will come up off and back into the seat a little providing a nice firm brace. And keep your Left knee snug to the F3's body. Your hips may twist a little, but your torso can stay upright with hardly any effort. When I do that, I never feel like I am being pushed off the bike - it feels more like skiing.
The other part of that I think most people miss is that you are Pulling the Left handlebar grip in and Pushing the Right grip/throttle out - not hard, but keeping it in balance for the turn and control of the throttle. That supports your upper body. I find I tend to lean a little left, but nothing like being on a bike and in a left turn that is mostly from tucking in my elbow from pulling the handlebars.
There is a lot going on ( throttle, handlebar, ready on the brake, ect. ) so take it easy at first, but if you "stand" on the peg, you should not feel like you are being pushed off the bike.
Tom