How to get over my tumbling mental block?

i have been working on my roundoff tuck for a few months now, and it is perfect with a spotter. my coach tells me to do it and they are to the point they are getting kinda frusterated i wont do it by myself. whenever i do it with a spot i know that i can do it and i tell myself i swear i will do it on my next turn to tumble. but then i get up in front to go and i tell the spotter to please just stand there and i will do it by myself i just want them to stand there just incase, but then i go and i dont do it. i do a roundoff and then either just rebound or a very sloppy back handspring. people say its a mental block but i dont know? and if it is how do i get over it quick? i have choreography in 5 days and i have to get it or i wont get to tumble in my routine. please help me :(