Biggest sail I can use?

Hi all,
I recently bought a new starboard Rio (s), After using it only a handfull of times I am beginning to think I chose the wrong sail size.
The package I bought was a ....Rio (s) board / Tushingham freewave 45, 430cm mast / 30 cm prolimit mast extention / Aeron 140-190 (I think) mct 29 boom / Tushingham storm force 10 5.5m sail.

I only started windsurfing two months ago but feel I should be going a lot faster.
I can't wait to get on the plane but feel the sail is holding me back.

So I am wondering If I need a bigger sail and if so what type/size should I go for?
Also would I be able to just buy a sail or would I need a bigger mast/boom ect: ?

I weigh 75kg
and the wind speed has been around 10-16 mph on the lake I sail in Wakefield.

Any help much appreciated :>)