How important is the SAT registration information?

I am older than the usual SAT applicant, but I'm applying to a school that requires the SAT and SAT Subjects.

When trying to register there was like 9 pages of questions about what classes I took in HS. Do I have to actually fill all this out?

Are the colleges going to know I skipped it?

I feel like I've already put the legwork into the colleges apps, don't want to fill out a bunch of junk on this site if I don't have to.

You absolutely do NOT have to fill out the stuff about high school classes. As this step-by-step guide to registering for the SAT notes, the only important information you need to fill out for SAT registration is your personal information (name, address, social security number, sex, date of birth), selecting your test center and test date, and uploading a photo that College Board will use for security purposes.