Only you can know if you overstayed or not.
You normally pay for the time that you input as stay; then, if you leave the parking bay late, your leave time is recorded on camera (or by the enforcement employee) and they send parking charge.
These parking management companies are normally technologically well equipped and challenging their data recording in court is normally quite difficult.
If you don't pay the reduced charge, it will go back to £100 and a collection fee will be added which is normally of £70.
If this goes to court, there is of course also the risk of being liable for the court fees to consider.
I hope this information is helpful and I wish you the best.
Please do not hesitate to contact JA again if you need help and you may ask to speak with me directly if you wish ("For TheLawLDN only").
I would appreciate it if you could provide a positive rating, if you wish so of course.
Thank you very much.
Regards.