Hi Joan
Make sure that you are setting your seams, ok if you don't know what I mean.
When you lay your unit of patchwork on your ironing board have the darkest side on top then press the stitches,(just sit your hot iron on it for a few seconds) this sets the seam, then carefull lift the top fabric and with the tip of your iron just gently press the seam allowance down. This makes your work sit flat
I hope I have explained that clearly