Why did you decide to join the debate club at the first place ?
Is is to work on your rhetoric abilities or is it because you are interested in a specific debate club ?
You need to know the answer to this question to be with sincere yourself, but either way I say - go and try it out.
You might not like it at all and decide not to come back again, which is legitimate, or you might find that the people in the debate club help you to open up and speak out, expressing you inner opinions.
I don't think you should be afraid to try out new stuff.