If you go just up and down and not back, it means you're not setting back and/or also your position at the end of your flipflip or roundoff or whatever you're doing before might not be correct - for connecting flip flop flip flop you want to kind of get your feet under after each one, for flip flop back flip you want your feet more out and not under you know.
For the setting for your back tuck/layout, when you're setting, make sure you're aggressive with your arms to your ears - set up, but also you kind of want to take the backwards motion with your shoulders for the rotation - not as much as a whip back, for back tuck/layout you want the set up higher.
Also, for the tuck and the layout, don't counter the backwards motion by you going towards your knees/legs - you want to bring your knees to your chest, not the other way around. That could be it too.
Check with your coach though! It helps also to watch the others do it that are doing it right and then try to copy them. :D