The method I use would be to cut your rectangle 2 1/2 X 4 1/2. Then I would cut two squares 2 1/2 X 2 1/2. Each of the squares then should be marked from corner to corner. Lay one square on top of the rectangle and sew it just a smidge inside the marking towards the outside edge. Make sure you iron the square back towards the corner. Then you cut the excess with a 1/4 inch seam allowance. Just cut the rectangle and the one side of the square. Then repeat for the other side.
Debbie