It's true about thinking "layout" but really, it sounds like your either buckling, twisting early, or maybe both.
Sometime when gymnasts want to get back as far as they can (like in a beam dismount) they "buckle" their legs. In essence, they bend them and throw their hips forward and their head back. Not only does it absolutely kill most of your speed, it makes things scary and not as good as they could be. To solve this, feel yourself set up and legs push off straight.
Twisting early is something that is scary, and very frustrating. Twisting early slows down your flip and, again, kills your speed. Really, the only advice I have for that is to go back and re-learn a later twist. Start with a good layout, then a good 1/2, and then you'll have a good full!
I'm sure you could imagine what happens if you do both...
When your coach is saying to think "layout", maybe he/she means for you to feel your set? This will help you twist later and go higher. When you feel your set, you feel yourself rise up in the air after your punch without making any other body shape until the set is finished. A set is important, so don't try to skip it!
Good luck, I'm sure you'll get it!
