Originally Posted by shnnn
Half square triangles have a bias edge, which tends to stretch - that's probably where your puckering is coming from. Starch helps, so does pressing not ironing.
That is what I was going to say too on the HST. In case you don't know: Pressing is setting down the iron on the piece, then picking it up and repositioning the iron. Ironing is moving the iron on the piece from side to side. It is easy to distort the bias edge.
As for the nubs where the seams meet: Sometimes you can take out the first few threads in the seam allowance and press the bulk open. It will look like a pinwheel and your seam allowances will not be one continuous seam. Instead it will lean toward the side that it wants to lean to. (Kind of hard to explain)
Another pressing tip is to plan it ahead a little so the pieces can nest in each other at the seam.
Well done, by the way!