one way to fix it is ...
Take a straight edge and a circular saw and cut exactly down the gap.
Then mate them together to see how they fit. If the gap is closed, reglue and clamp. If not, recut the gap until there is a perfect fit.
As long as the saw blade goes in a straight line and is square to the surfaces you won't need a jointer.
Always apply a finish to both sides of the wood to prevent uneven shrinkage and expansion.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 03-07-2014 at 06:40 AM.