Number one suggestion would be as previously suggested to remove the luff, move it back a couple of inches at the top thus reducing the length and resew. Easy job and a long straight sew.
Another method might be to unpick centre
horizontal seam, remove the necessary length and resew. You would then have to cut and resew the luff and leech from the new horizontal seam back down to their respective tack and clew but all the stress points,head tack and clew would not need any work/alteration and all the
fabric tensions would be exactly as designed. The bolt
rope would be cut at the bottom and resewn in as part of the luff resew. Quick easy and once again straight sewing.