This Saturday I'll participate in a charity run where you find people sponsoring you and they will donate based on how many laps (400m) you manage to run in 2 hours.

My longest run so far was a 10 km run with a pace of 5:30 (very exhausted afterwards) and once with a pace of 6:15 (felt like I could have gone another 30 mins, however my HR steadily climbed from around 160 to 180 at the end).

My two questions to you experienced runners:

1. What would a good strategy for running the longest distance possible in 2 hours?
2. Is my HR an issue? It didn't seem to really stabilize and was around 180 for the last 10 mins. Will it plateau if I run more than the 60 mins or will I run out of energy before?

PS: I know running that long without proper training might be stupid but I'm determined to make my sponsors pay.