ステッチ方眼紙

I do very large and very detailed cross stitch work with lot of backstitches, 1/2 square stitches and beads. There are not enough symbols to use or the option for 1/2 square stitches. Please fix this since I had to pay for this app.

Why, for the love of god, is there not an undo feature? It also really needs the ability to backstitch diagonally over two or more squares. Even just to be able to draw over top of the pattern would be great. And the Apple Pencil can’t do one square at a time. I can draw several stitches with it, but have to do single stitches with my finger.