Should I play Fullback in the 9th Grade?

I think fullback would be perfect for you, you just will have to handle the pounding that can come with the position. If you've played RT, then blocking should come more natural to you, and that should be your first focus for the running back behind you. A blocking FB can easily become a running backs' best friend. Plus FB runs are not used as often as they use to be, so when they are it can often surprise the defense and get decent yardage.