Try really starching your fabric prior to any cutting. I find starching ( very heavy starching) is very helpful with paper piecing. It helps to keep the biases in check and once the fabric is folded and pressed , and it is less likely to fold back on itself ( I really hate when that happens).
Once the block is done before removing all the papers stay stitch around the perimeter 1/8 ich from the edge, using the same small stitch length you used for the rest of the block.