Help with my singing please!?

When I sing my voice always crackles on a high C# it is annoying because the song I am currently working on (Down to Earth by Justin Bieber) contains a lot of C#'s. Is there anyway I can sort this out? I'm not a very confident singer anyway and I have to sing this song in front of my music cl and I'm very nervous, any help with this too? btw, I can't change the song, it is too late. Thanks!!