I'm not an expert, but what you really have to do is be confident. You can't let your tumbling control you. You can't be scared of your tumbling, because if you just move your body in the right way you can't get it wrong. It's easy!
Don't try so quick to tumble. Before you throw it, picture the skill in your head. Tell yourself the exact same words above. That's what really helped me.
It always helped me to have the pressure taken off. If theres no immediate pressure to have your tumbling back, its not so scary. Take it slow, build back up.