Shooting for 8 miles in 2 hours today! My goal is to burn 1300+ calories because I don't have swim tonight! The downside is I go

Shooting for 8 miles in 2 hours today! My goal is to burn 1300+ calories because I don't have swim tonight! The downside is I goofed up and drank a ton of water when I woke up so I couldn't get an accurate weight this morning (why must water weigh so much >.