I'd stitch in the ditch from one side to the other to stabilize. (Go right on past the corner stones) But I would not cross over the sashing with your lines inside the block. It appears that the sashing is narrow enough that putting any kind of design there would be "too much" and not necessary. Wow--you did great as a beginner! I didn't notice any blocks with the points disappearing. Interesting blocks, too. None were easy. Keep up the great work!