My suggestion would to just jump on party finder and setup a learning group until your comfortable with that encounter. There is no expectation of performance in a learning group.

If the endgame stresses you out too much I would just not do it, and stick with things your comfortable with. DPS don;t usually get a lot of commendations people usually give them to tank, healer, or not at all. I usually try to give it to a random dps tho.