Your story is very similar to mine. I too paid up front for a single JM AFF course and after 4 jumps in 1 day was asked to leave. I was returning to the sport after a brief 25 year break and was confident I would sail right through. My jumps were not that bad and I as I passed each level I thought I was on my way. I was not cocky and was open to criticism, so I was kind of shocked when I got the boot. I went to another and much smaller DZ, explained what happened and was given the chance to start over. It was one of the best decisions I ever made. I am just waiting to do my A check dive now.
( I also spent 15 minutes in the tunnel)