OP, you must acknowledge service of this claim (AoS) no later than 2nd March. There is no advantage in delaying the AoS. By doing the AoS, you then have until 4pm on Monday 18th March to submit a defence as a PDF attachment to an email.
Ignoring this would not end well for you. However, defending it is not difficult.
Do you still have the original Notice to Keeper (NtK)? If you do, please show us, suitably redacted of personal details, PCN number and VRM but keeping all dates visible, we will be able to analyse your situation a bit better.
If you can get some photos of the signs at the location, that would also be useful. It is interesting that PE now add £20 to original charge of £100 without justifying it, as far as I can see.
Did you contact the hotel management and complain to them about this invoice you received from PE? Were you a patron of the hotel?