DJ
Several issues here.
First is board is probably much lighter than your old one, making it feel jumpier underfoot. I really noticed this getting off an old Bombora (15kg) onto a new board (7kg). The Bomby was like a torpedo through the chop - the new board wanted to leap over every little ramp. Eventually you will grow to love this new feeling.
Two such a small sail will not have sufficient mastfoot pressure to pin the board down. I weight 105kg and don't feel comfortable on a 98lt board with a 5.0 sail, so a 4.5 with a lighter rider would feel even scarier. I find a 5.4 borderline comfortable, a 5.8 feels perfect and a 6.2 very good on my 98.
Three push base to front of track to try and hold nose down.
Four, get a smaller fin because it's possible in such strong wind you may have had too much lift from a 28, which could lift the whole tail out of the water. With less lift, the tail sits deeper, aiding control.
You may wish to consider buying an old wave board with about the same volume as your body weight for these wind strengths and such small sails - they are usually pretty cheap and you will have all the control you would wish for. Maybe an old plastic Tiga which are cheap as chips, are indestructable, and heavy enough to slice through choppy conditions ?
