Just wanted to re-iterate what everyone so far has been saying.
I used to have the same problem as you when I first started too, but the thing that really changed my perception was to realize that you rarely ever want to flat base. And the faster you go, the worse it is to flat base because then you don't have as much control over your board. It starts to shift and get all squirrel-y under you.
A good thing to practice this season would be to start always staying on an edge as you pick up speed and start making your carves as straight down slope as possible. Once you get comfortable with that start bringing your board back down closer to flat base but always keep pressure on 1 edge at all times. Once you get the hand of this it will be second nature and the only times you'll ever truly flatbase from here on out is off the chair or maybe when you're just cruising along at a snail's pace.
Mmmm dunno if I agree. I have flat based at massive speeds. It's about keeping your weight over your front foot and your shoulders in line with the board. If you are on an edge you are washing speed off