We have a policy of not doing other people's homework, but we do offer hints.
Usually when I have a well-formedness problem like this that I can't solve, I make a copy of the document in question. Then I take the copy and start removing sections that I know are good. Eventually, I'll isolate where I went wrong. This is a technique that works really well in any scripting language, too.
Another option is to use an editor that supports either code folding or syntax highlighting. Komodo Edit does both, and it's free: I've used it for years. I suspect that with code folding, you'll find the error within minutes.
