As foundation paper piecing means that you work from the back of the finished block, it can get confusing where there are diagonal seams and you have to check each piece of fabric to make sure that when opened out that there is sufficient coverage. So instead of cutting chunks of fabric in the hope they will fit, instead, trace the paper pattern roughly onto freezer paper. Remember to transfer the letter and number labels from the pattern and straight grain line arrows help too.
Cut out freezer paper pieces, and iron to the reverese of the desired fabric, in this case a background print. Leaving the freezer paper on the fabric, cut out leaving a 1/2" seam allowance all round. This generous amount gives you a little wiggle room.
Place on to your foundation pattern and sew as you usually would, it helps to leave the freezer paper on to identify the pieces as you go.
You can see how the fabric for piece A3 is ample size and opens out to cover the area and the 1/4" seam allowance with a little extra left over.
This technique saves time overall as you shouldn't need to unpick and pieces because they are too small and to be honest I do this every time with diagonals- even if it is just making a quick freezer paper template for a single piece. I hope that helps!