I know it's too late, but just as a pointer...
I've been singing for many, many years, and here are a few rules for singing:
1. It does not matter how you sound. I know that sounds crazy, but it's important, and actually true. You can dress up your voice however you want, but on the high and low notes (unless your song is "stalemate", with no pitch change), the key is to stay strong.
2. Supporting #1, you should go over a song before you sing, and note where you are going to breathe. The worst thing you can do is choke on a note.
3. Practice getting out of your range, so you know you're not stretching all that much.
4. Choose on the high notes whether you want to go into your head voice (masking the notes with a soft tune), or try and shoot for the risky high register (focusing projecting the notes out strong and slightly masking with a high accent).
That's my advice for next time.
Mods please let this through