Stall more and try to keep your body tighter in "one piece". Twisting "harder" will probably make it worse. Basically in terms of physics, twisting doesn't increase rotation for an object but for most people twisting harder entails shortening the axis on one side more which increases rotation. This works to some extent, really, but too much and you're on your back. Ideally the body would be tight, the flip would be high and "stalled" out after it was initiated, and the twist would come more from the movement of the arms. You can see this really well in trampolinists doing a full or double full (single flip).
Also the arm motion and twist should come in somewhat "hollow". It's really hard for me to explain it in words, makes a lot more sense with demonstration, but I'll try. This is easier to see on floor but applies to bars to some extent. As the flip is initiated, people tend to throw back into the full with their shoulders as they pull their arms, rather than set up and pull in hollow to keep the vertical momentum. On bars the initial shoulders throwing back isn't really much of the problem because of the release usually, but I do see a lot of people who pull their arms in a way that throws their shoulders back as the flip is completed, causing them to land on their back, instead of maintain a slightly hollow position through the chest and shoulders as the arms work.
If just trying to correct technique doesn't work, it might to help to start again with layout flyaways. Release (shoulders open, toes leading up and out) and as you come around and see the floor, pull your arms down to your thighs with a hollow position. If you have a pit you can start working on this and then basically try pulling down hollow to the side you twist to initiate a twist at that time and see if it helps you stall the flip. After that you can kind of move to a "one-two" motion in the arms for a full twist.
But there are a lot of different schools of thought for teaching and doing a full twist, so maybe someone else's idea will work better for you. These methods work pretty well for me, but I have seen people learn and teach it successfully other ways.