I see now that this is the Lava Pit map (Gravel Pit), attack/defend. If you're all by yourself on BLU, here's what I would do: Set up a full Engineer teleporter/dispenser/sentry to help the arriving BLU players quickly get to either A or B once they arrive. Defend the area around one of the capture points, but don't cap it yet. If the timer is about to run out, capture the point and then set up nearby the other point. Stall and run down the clock until the GC sends more players. If you have to stall long enough that you capture C, then set up a full defense on RED while you wait. Then, if the match gets completed, you get some XP credit and can then requeue.

If the map is popular enough, the Game Coordinator will eventually send you a server full of people. In the meantime, set up a full Engineer defense and wait for them to come, especially if it's a KOTH map!