I hate starch and never use it. I've also made many bargellos. If you "make" your last two strips come together you are going to have bigger problems down the road. Don't try to force it, just sew it as best you can. You will lose the fabric on each end as you cut cross ways of the fabric. If you force the seam, you will wind up with diagonal pieces, not squares, which you can't pin out as you sew the rows together. They will always look like a diagonal.
Somewhere on my home computer I have basic instructions, with a lot of pictures, I would be happy to email you. My quilty friend who sews far more than I do had never made a bargello. I taught her how using email. PM me if you are interested.