As @PrincipalTinker said, you can only book either RnR or TSMM because Hollywood Studios has wonky tiers to make you pick between headliners. Epcot does this, too. Fpps are booked in hour blocks, so you could book TSMM from 9-10, but you’d have to book a tier two like tower of terror from 10-11. If you only make one choice, Disney will pick the other two. But, you can delete selections on the website (not the app–that deletes all) before arriving.
Once you use a fpp, you can try booking another one. What I’ve done in the past is book tower of terror 9-10 and TSMM 10-11. We’ll hit TSMM right at rope drop, then head to RnR, use the fpp at ToT, not terribly important this early in the AM,but every minute helps, then go back to TSMM with the fpp. Once we are off TSMM, we’ll visit a kiosk and see if anything is open and get another.