Katt stick with the park run, one day you will get a dry surface and you'll smash your PB!
Do you start near the back? I have seen loads of beginners go off really fast and then struggle later on. When I started parkr run I used to take a short walk break, then I started trying each week to take the break later and later by going a tiny bit slower on the 1st kilometre.
I did the 5 miles on Saturday, a few seconds under 50 minutes so I was chuffed with that.