I am a big fan of Sun Bonnet Sue and have several quilts showing her off, also made a few mistakes (or at least I thought so) using yellow fabric in quilts, it does tend to take over and become the focus fabric, however, using it as a background for Sue is good, she really pops on that yellow. But I would suggest not using more yellow in your borders, instead use the blue/purple, pink or any other color from your pattern fabric, or a different variation of pattern fabric, but limit the use of yellow otherwise it might draw the eye toward the border and you want to keep the focus on Sue, which you have done nicely, good job!