You have now reached the last nail (nr 10 in the drawing). The last stitch through sideloop 9 is made, and now you have to do 1 more single crochet, if you want 10 stitches on this side. And that’s exactly what we want!
On this picture you can see that I made 23 stitches on my loom. If you have a loom with 10 nails, you would have seen 9 stitches here. You count the stitches by counting the number of V-shapes. In this picture the first stitch is marked with a pink stitch marker.
Because you have no loop in corner B to work through, you will make a temporary loop there, by working the end of the yarn into the weave a bit, around the corner nail. It doesn’t really matter how you do that, because, when finishing your weave, you will take it out again, it is purely for having a loop that you can crochet through!
Now make a single crochet in corner B:
This is the first single crochet in corner B, which is also the last stitch for this side.
Now make the second single crochet in corner B:
Mark the first stitch of this side with a stitch marker again. It’s the V-shape you made last and that’s right before the loop on your hook.
Now again make stitches in each sideloop until you have come just before corner C.
Go to the next page for an explanation how to deal with corners C and D.