That's right Sazu, pressing down without moving the iron around too much will keep your square in good shape. For me, the thing that can throw my block out of kilter faster than anything else is not keeping a consistent 1/4 in. seam. My machine that I use the most for my piecing, my old workhorse 38 yr old Kenmore, it does not have a quarter inch foot. But I made a mark where my fabric should line up to achieve that 1/4 in seam allowance and that's my bit of advice.