If you have ticked the box for the 3 free relists when you listed the item, you will need to turn that off before ending it.  Just find the item in your selling list on your MyeBay page and click the menu list at the far right of the item.  The last item on the list should read Remove autorelist, click this and then end you can end the item without it relisting again.  You should find if you check your account though, that you have not have been charged for the relist, if you got an autorelist message, it obviously hadn't used up all three free relists.