Table Of Contents / chapter heading

I have tried to search the net for answers and have found nothing. Hopefully you can help me.

What I am trying to do is make my three ebooks formatted the same. My first issue is that when I compile, the chapter head is slightly more bold in the Kindle previewer than in other books. I have been looking at settings for hours, and have determined that all of the settings are the same for each book, but the chapter head on book one just looks a little bigger and bolder. This is so frustrating.

My second issue is that I cannot figure out out to center my table of contents. It is centered for book 2 but not book 1 and 3 and I have no idea why.

Can someone please help me with this issues? Thanks.