To help you gauge, the floor at the Molson Amp. holds about 1,000 people according to Wikipedia. The covered seats (so the 200 and 300 level) hold about 5,500, the uncovered seats (400 level) holds about 3,500, and the lawn holds 7,000.
Also Chris, did you see the main stage area at all? I would assume your booth would have been in the second stage area, which isn't that huge at the Molson amp grounds, so it may have looked packed there.