So you can't enter the tournament at all? Or do you mean that you were defeated and lost the tournament?
If you can't enter the tournament then check if all 6 puppets in your team are over level 50, because I'm pretty sure that's a requirement. If you were defeated and can't reenter... I'm not sure what I can do to help.
Oh and the tournament keeps track of your whole team when you enter, not just the three you used in the matches you entered. For example: if I had Speed Flandre, Assist Koishi, Defense Nue, Speed Remilia, Defense Tenshi and Speed Youmu, but only used Koishi, Remilia and Youmu in the first five matches, then opted to leave at the checkpoint when asked I'd still need to bring Flandre, Nue and Tenshi to reenter the tournament even though I didn't use them in any match.