the thing is that when I’m going let say 50mph and go down with throttle instantly boat wants to go the right . So I gently put trottle so it doesn’t do it . I think that a problem of cable steering ?

Boat on the trailer/out of the water, go back and grab your drive and wiggle it side to side. How much play does it have?

There is like 3inch of play left to rite and 2mm up and down .

3 inches of play? There's your problem.

I don’t have external steering.
I thought it’s normal with external steering

I had the same issue. Play in steering and pins.

You need a new gimbal ring and steering pin.

Exactly. 3" of play is NOT normal at all. This is your problem.

I would not mess with an extension box. Fix your worn components.

And while you are at it, I would go with a dual ram Imco hydraulic steering. Do the full kit from helm all the way to the outdrive. The wider the footprint your transom will allow, the stronger the setup is.
https://imcosteering.com/imco-catalog-2022-v10.pdf

Ok understand, someone suggested the Merc ITS which I really like but can’t find a used one that I can buy. also saw the imco with wings that like too because don’t really want to do holes in the boat .

why don’t mess with extension box’s I see all fast boats have them 😃

I put a Mayfair box and steering on my 26. Up 2" plus a 2" imco short lover, so x is up 4". Haven't run it yet, so no real input for you.