Thank you for all of the replies, they are really helpful.

I'm glad to know I was on the right track with the things I was trying to fix it. I suspect I didn't practice it anywhere near enough before my first attempt at recording it. I think I was still figuring out how I was going to sing it as I recorded it, which I suppose was always going to make fixing it an uphill battle!

I'm going use all of the advice in my next attempt at recording and hopefully I'll be able to actually finish the song and have something I'm happy with!