If the last seam you sewed was the up-down one in the picture, then just sewing over this seam taking up more seam allowance should fix this problem. When you are making a seam deeper, you can just sew again -- no need to rip out the first one.
If the last seam you sewed was the left-right one, then it looks to me as if your seam allowance was too small when you sewed the two half-square triangle blocks together. You would have to rip out the last seam, then re-sew the remaining two seams with a wider seam allowance.
Also, it looks as if these blocks got a lot of handling. Starching before cutting and/or starching when ironing seams should help prevent the pieces from being stretched out of shape.