A rumour about me sending nudes has been spread! Help!?

Don't worry about a rumor as in time it will be proven unless you did spread them.

Just ignore it it will die a natural death, unless of course you did do it

If you're in school (which you most likely are), try going to the principal and telling him/her about the rumor. S/he will try the best they can to help you. If you know who started the rumor, try confronting him/her. Not necessarily in a bad way, but try to be assertive. Ask them why they spread it and express your displeasure with it. Of course, this might not help all situations because the person who spread it isn't going to want to help you obviously. But, if you can make peace with him/her, you can fix this. However, if you cannot make peace, just make sure everyone knows you don't send anything like that. As long as you and your friends know you don't, you shouldn't worry. No one else's opinion matters; after all, people are going to talk about you, no matter what. No one can make you feel inferior without your consent.