can I be fined JUST because I didn't appeal within 28 days

Half_way

The so called time limits area also entirely arbitrary, in other words the pay, or "appeal" within 28 days is a rule that private parking land has made up in an attempt to try an emulate real parking tickets issued by a real authority

Coupon-mad

No idea why we still have threads from people who haven't read the NEWBIES thread and have no idea about private parking charges and how to appeal, or what to do to beat it if they have not appealed.  Sign...this is completely covered in the NEWBIES thread and of course no-one pays hundreds of pounds.

If you are using a phone to 'view' the forum, take those blinkers off and look at the advice at the top of this forum board and use a PC or laptop to read what to do.  You haven't even said what happened when you (of course) complained to the Gym in the first instance and asked the manager to email the scammer to cancel the PCNs.  As anyone would, without needing us to tell them to complaint to the landowner.