In reply to kingjam:
If you can't increase your climbing volume, you won't benefit from a fingerboards - as the others said, it's useless below a certain level.
If I were you, I'd focus on volume. Start by measuring how much you can fit in that weekly training session: how many moves, how many routes, how many problems or how many meters - in short QUANTIFY it.
Once you have those figures, try to increase them progressively.
For instance, if you can climb say 5 no. 6a routes of 15 m, then the next time, make sure you climb 6 of them, or try a 6a+ or choose longer ones.
Make sure you meet the target without increasing the overall session time spent (tip: drink plenty of water between each attempts).
If you keep track of those numbers and push them up during that weekly session (make sure you don't waist it by chatting around), then you should easily gain a couple of grades and improve your technic without any serious risk of injury.
I'm no climbing coach, but to climb 6c indoors, you don't need any