What's the volume in the board? I'm 100kg on a Seatrend 100 (180l), and it's very stable (compared to my 73cm wide Fanatic) and not quite as stable as my old 110cm Starboard Start. Perhaps you're time away from the sport has compromised your balance? You've also got to remember that all the volume is at the back - mine sinks at the nose if I dawdle around the front of the board during a tack.

Eckas

This is my opinion
On assumption you are a beginner.

This is a full-on Race Board.
It is made for advanced sailors. It is light and the construction is good for those who know how to treat it right.
The huge fin is needed for the big sails it should be holding like a 10.5m.
It will not be easy to learn to carve gybe on. I can carve gybe better then most and to me it is still hard work to gybe.

You cant just judge a board by its volume, you have to look at other factors too.. ie outline. shape, rails. etc

In my opinion you would be much better to get a Bic Techno of some sort with a plastic shell that is a lot better for little knocks etc.
New they are about $1000.
2nd hand could be anywhere from $400 to $800.

It will be alot easier to progress on


You have bought a formula rally car rather then a little excel or similar to learn on.
The Kinetic will be great when you get to that stage.

Even with a 1m wide board it's going to be hard work getting it going with only an 8.3 and your 105kgs. My guess is you probably need a bigger engine and some more horsepower. I notice there are a few people trying to sell larger sails on the buy/sell forum with no buyers, so it maybe a good time to buy a 10m+ rig.