Open water swimming tips PLZ =)?

im a lifeguard, well allmost. I have to pass one more test which is a long swim in the open water. The swim is 500 yards and i can do it in a pool EASY, but yesterday i tried it in the open water, i barely made 2 yards. When i swim freestyle in the ocean, i dont see anything, my eyes hurt, i constantly change direction, and the waves keep hitting me and messing up my breathing. What should i do? any tips?? i have couple of days til the test.