Where is the question "were you a full time student?" I accidentally clicked the wrong box

I would suggest you to return to the Form 1098-T section and follow the prompts.  

In TurboTax online,

• Sign in to your account, select Pick up where you left off
• At the right upper corner, in the search box, type in "1098t" and Enter
• Select Jump to 1098t
• Follow prompts
• On screen, What Was your Enrollment Status for 2020? check your answer

The definition of a full time student is "as defined by the college".  It further states that an "at least half time student" is one that is enrolled in at least half the workload of his or her course of study, based on the institution's definition of what constitutes a full time student.  Per IRS publication 970, a student who was enrolled at least half time is considered as part of the requirements to qualify for the education benefit.  

The full time student question also appears in the personal info section.  You may need to edit there too.