A friend of mine is in a district where 8th grade math is algebra, honors is geometry.
In terms of gaps - I wouldn't be too worried about it. In a lot of places 7th grade math is basically a repeat of 6th grade, and it isn't until 8th that there are some big differences. However, gt kids who are advanced in math usually fill the gaps on their own as they learn the new material. If it would make you feel better, you could always just talk with the math teacher at the beginning of the year and explain the skip and ask if they would inform you of anything that seems to be missing and you could have him fill it in at home.When our DD skipped a few grades it was just really a matter of speed as opposed to understanding that held her back at first. She hadn't had the time to really cement the processes in before she was applying them in her higher math class, but she quickly got over that hurdle and did fine. In fact she liked the harder math because it was more interesting so as a result she didn't even notice the gaps as being an issue, and neither did her teacher.
Congrats on the course assignment