What Carl said is so true. The mainsail for a sloop boat has a different cut than a uni. For sloops the draft at the top is around 30% and near the bottom, it is around 50%. The reason for the difference is to accomodate the jibs overlap.
Take away the jib and your sail is cut wrong. It should be Somewhere between 30 and 40 % aft all the way down.
So, if you are going to remove the jib, you will probably need to get a new mainsail made.

A great and fast rig for single-handing would be a main, with a self-tacking, roller-furling jib and roller-furling spinnaker (Hooter or Reacher). Hot boat that is easy to operate.
Good luck,
Rick