Make your center and then see how you feel about it. We joke about 'your quilt will speak to you', but it is often true. Also, you may find you don't want to make any more of the HSTs and simply want to put on some borders. Or, you may be having so much fun with them that you want to go on. Many, many, many of our quilts are planned to go one way and they take a bit of a turn and end up a little different than the original plan. It's all ok, it is your quilt and you get to make all the decisions about it.