I need help with a star blanket

• Hi,
  

I’ve crocheted a star blanket and now want to close the corners so it becomes a pentagon. I’m a relative beginner and have no idea how to do it. I’ve already tried crocheting back and forth between the corners (using half double crochets). Crocheting a triangle that I could then sew on didn’t work either—I couldn’t get the angle right.
Can you help me? Maybe with a photo tutorial and a really detailed explanation? Maybe the back-and-forth crocheting method isn’t so bad after all, but it just isn’t working for me.

If you start the triangles with one stitch and then increase exactly the same way you decreased for the star, shouldn’t the angle be right?

Hi ruthk,
thanks for your reply.
Your idea is good, but unfortunately I can’t seem to make it work.