High school rank, GPA, test scores are the 3 key criteria listed for Nursing applicants on their admissions site.
https://www.clemson.edu/cbshs/departments/nursing/students/prospective-students/prospective-freshmen.html
It looks like you’re on the right track. You might try reaching out to their admissions to see if they can offer any statistics for qualified applicants around those criteria. Not all high schools rank. A 28 ACT is respectable but you might check with them to see if it is competitive for nursing. Also recommend you take SAT as some students fare better with one test type over the other. Also, take these tests more than once as Clemson super scores (takes the best sections of all your test dates for each test type to build the highest score possible).
Good luck!