How to explain social prescription for gym unsuitable?

The rheumatologist recommended a social prescription for gym membership for fibromyalgia. I really tried to access this but wasn't able to. Is there a good way to explain why?

Basically the person who did my induction told me the wrong time and then told me off when I arrived at the time I was told. She was off-hand with me and didn't actually tell me where the classes took place or how to access them. When I tried to book something all the classes were already full. The car park was too far away and I was exhausted just walking from the car park. My fatigue is really bad and I just can't manage a regular class at a regular gym. If I put that I couldn't access it as it was too difficult and I was too exhausted, will that be ok?