Those wide spaces are an error in the HTML code that you can't really do anything about at the moment.
As for your fic, it's just as Richard said, mostly average with room for improvement. The errors aren't very large or noticeable, unless you're a grammar nazi, which I am. It's an interesting point to start diverging from canon and I look forward to seeing whether or not you can successfully do it.
I'll write a real review for you in a few chapters after you have a little more to read.
Author's response
Thanks for the info. This was originally my NaNo project for the year, but health reasons kept me from getting too far into it. At the moment, I'm working on Chapter 3 and looking over Chapter 2 for errors. Chapter 3 is where the crossovers start.