Use the current - don't fight it.

I've been caught in a similar situation at that marina myself. I'm not sure I can visualize your situation but I have found using the current can often help in close-quarter maneuvering.

Simply point the bow into the current and adjust the throttle to match the current before you approach any obstacle. Now you are holding your position over the ground. Manuever by steering port and starboard and adjusting the throttle. This gives you precise control.