Before you submit either type of evaluation, you need to get your certificates stamped and signed by your school. You can only use your transcripts, the grade report sheet you got on results day will not be accepted. This may be difficult from the US so you may need to send a few emails to an old teacher/Principal/exams officer or ask your parents to pop into your old school.
Take colour photocopies into your school and ask a teacher/Principal/exams officer to stamp and sign the photocopies. Then take clear PDF scans of the stamped and signed transcripts. If you or a parent absolutely cannot go into school, take clear scans of your transcripts, email them to a teacher/Principal/exams officer and ask them to print them, stamp and sign and scan them back to you in colour. You will need to ask someone you got on very well with to do this as it is a lot of work, you must ask politely and explain how important this is for your university. Your certificates need to look like the below to be accepted by the evaluation companies.
A-Level Certificates look very similar to GCSE certificates
You need module pages with BTECs