First you are going to have to make sure that the length is going to be good. I think a King is longer than a Twin, so you might need to add some length to the pattern. If you purchase an additional length of the background, you won't double the size of the quilt. To do that you would also have to duplicate the pieced rectangular section, or add an additional piece of background that would be the same width. I think you are going to have to do some math and compare actual measurments.