Having just pressed my newest top, which is 96 x 116....I would just say it is impossible to make it perfect. I just pressed mine as well as I could, dusted off the corners that had been on the floor (I swear, I just swept the floor!!!), and moved on. I did go into it knowing I couldn't keep it as pressed looking as I wanted. It's okay although, since I quilt on my domestic, I knew it was going to get scrunched anyway.
No help am I? Well, the way I actually ironed was across.....I'd iron and then move the whole thing horizontally....then move it down and do it again.
Good luck. You can do this.
Dina