I had carple tunnel realsea surgery on tuesday i've just taken the bandage off and had a look . that is a split down the center?

There will be: a sutured or otherwise closed surgical incision if that's what you mean by "split" but it should not be open. As I am uncertain what your definition of split is exactly, if you believe the wound dehisced (opened) then contact the surgeon immediately.

Surgery : There would be a cut from where surgery would have been done . There should stitches along that cut .

Yes likely: This is where they will cut to release pressure on the nerve. As long as the skin edges are together thats fine. If the skin is pulling apart or you have concerns please seek GP review and please seek urgent attention if the wound is red, angry, you feel unwell to exclude infection