Screw the blank to your faceplate, turn the bottom/outside of the bowl. Be sure to leave a good flat bottom to glue to the faceplate.
Screw a piece of scrap wood to the faceplate, turn it flat and smooth, glue your blank to the wood face with a piece of brown grogery bag paper between the two. Rotate the lathe by hand to be sure the bowl is centered on the faceplate, let it dry then turn the inside.
After you turn the inside of the bowl you can pop it off with a flat chisel and sand the bottom by hand or on a belt sander.