The issue you have is the same as me. You cannot maintain the pace and persistence needed to complete a full day of work. Yes, you can do short stints of the tasks you need to do. BUT, you cannot complete the equivalent of 2 - 4 hour periods of work like a normal work day. Plus, you cannot be certain what days your mind is up to the task of getting even a few hours done.

I can get a lot done if I have complete control over the pace. I cannot function with time pressures. I can work for a hour then take a break and return when my brain is back to work. If I need to do serious thinking work, I can get a few hours done over the space of a day. I bet you are the same.

Do not try to work about the stresses of the test. It will only make the result unreliable. Roller coaster results will confuse the test scorer.

What clinic/office did the testing? If I remember, you are in Texas. There is a great concussion doc in Dallas. I think his name is Walker. He does neurofeedback, too.