The reason for the tile extending past the edge of the tub is to allow for the "bullnose" edge pieces to cap the backerboard when it's installed as a second layer (over the drywall). It also affords some protection (waterproofing) for any water that may get past the shower curtain. Water running down the edge of the tub on plain drywall will take a toll after a period of time. It will rot the drywall AND the baseboard. You CAN install your tile as shown. I wouldn't recommend it. You culd be creating problems down the road.....