Hi Ingrid! Thanks for your help. I don't understand:
The M1 shouldn't leave a hole. Are you knitting into the little loop in the back or the wider strand in the front?
I knitted into the wide strand. Is the "little loop in the back" the stitch from the previous row?
But I do understand your other instructions. Thanks, I'll have a go!
(I think it will work best if I do it on the odd-numbered rows after finishing full "rectangles". In a mid-row increase, I'll inc in two stitches.)