We talk about a 1/4" seam, but you don't measure the seam, you measure the resultant patch. Others have posted about this and here's a tutorial:
http://www.quiltingboard.com/tutoria...ce-t89997.html
If your blocks are too small either your seam is not correct, or you are pressing a tiny crease in the seam.
I have a steady betty and really like it. My cousin bought the one that covers an entire ironing board, but didn't want to use it all the time, so she cut it and gave me half. I don't use it for yardage, just for pressing blocks. Having said this, it's not going to solve the problem of your blocks being too small. It does help keep blocks square, especially those with lots of seams and/or bias seams.