I have not read Izy's tute, so I am not sure what advice she has given---though I am sure it is spot on. So, forgive me if I am just repeating what she said.
When I chain piece, I butt the next pair of fabric squares right up to the one on the machine bed. Do not wait until you have one pair completely sewn before putting the next pair in.
When you have pressed your seam allowances in opposing directions, they are easy to snuggle up if you have chain pieced closely. I also find it helps if the top seam allowance is facing away from you when you feed it through the machine. That is not always possible, but it does help snuggle the two seams close. I never pin and mine match perfectly 99 percent of the time.
Keep practicing. Soon you will be "perfect" every time. But, remember too---"Better finished than perfect", so don't drive yourself too crazy!!