Without having seen your rig I'd say Sailpilot is right, chances are you need more downhaul. I used to worry that I'd break something if I downhauled any further, but trust me you won't... in fact you're less likely to break something because you'll be less likely to catapult.

As for that out of control feeling, where are your straps positioned on the board? If you put them forward and inward, you'll probably find that you have a lot more control once you're up on the plane. Once you get more comfortable and want more speed, then you can start moving them outwards and further back.
Presuming that you're using the standard 28cm(?) fin and that you're not sailing in ~30kts, then I guess the only other thing to check would be that centre board is all the way up (are they removeable on the Funster?), otherwise you'll be fighting it all the time when you're moving at speed.
To answer your question on mast position, generally speaking 'forward' is for control and early planing, and 'back' is for speed and manoeuvrability.. the link below explains in a bit more detail.
http://www.boards.co.uk/articles/index.asp?ID_A=191&article_type=25I don't necessarily use the measurements.. but the article explains about board trim etc