Perhaps this... Your bed is approximately 60x78. You have the width already covered by your stars. Add a row at the bottom to give you a bit of length then put a dark blue star fabric (Civil war era) or dark red star pattern solid border all the way around to give you the overhang you desire for your bed quilt. 90x100 is a good size overall but remember, a border just frames the design of your quilt. I design the interesting parts of my queen size quilts to be 60x72 and then use the border to emphasize the work I did in the main pattern. It also helps me make the bed. Easy to get it right, first time, every time. LOL. Funny thing is, since I made my first quilt for MY bed (and didn't give it away), my bed is usually made in the AM because I like looking at MY work.
tim in san jose