"Send an e-mail" when participating without an account seems not clear
When participating without an account, the button say "Sent an e-mail" (envoyer un email)
For me (but I am no designer) it seems not totally clear what it will do. I want to participate, not "send an email to whoever". I suggest a more classic "Participate", and perhaps a small line ("you'll have to confirm your email and the organizator will have to validate before you are fully registered")
(It is a suggestion, by no mean I want to devalue the nice work done here and you are far more competent than me to choose the right text).