Check this on a piece of paper but I think you can make doing a Rail Fence. Each half yard is 7 2 1/2" strips. Put a strong color on one edge. Sew the four colors together, measure the height, should be 8.5. Cut 8.5" blocks from the strips. This is the sticky part. If you can get five, you're golden. If you can only get four, you'll have to piece four ends together to make two more. An extra seam won't show when it's quilted if the colors and seams match. Put these 8.5" blocks together in the RF pattern - With the strong color zigzagging across the top diagonally. 5 blocks across (finish at 8" ) and 6 down gives you 40 by 48. Use the FQ for binding. You'll have enough if you don't make it double. Sounds good on paper, but check my figures before you cut. A bit from your stash could be added for a narrow border, but keep the finish under the width of the fabric.
We do our prayer quilts 45 by 54 or 60. Not overly large to me, but the recipients feel they are just right.