The hovercraft sucks yeah, it takes lots of practice to get it under control.
At the corners slightly change direction just before you would do normally in a car, and well don't expect it to act like a car anyway.
Don't expect the hovercraft to ever go the direction your face is looking at in a corner when you're in a corner to the left and looking a bit to left-front, then you're hovercraft will most probably just go a little to the right, tap the direction buttons securely to stay in the corner.
Don't turn to much, if you're about to crash a wall, you're most probably tend to turn to the other side untill you go to the good side again, but this will result into going from side to side all the time as you do. Just release the A button and slidely move the other way without turning to much the other way so you won't hit the other side again.
For the rest it's just mostly getting used to it and it will never drive as good as a car... If you really can't get any further you might also try to just collect some coins in easier races and use them to upgrade your hovercraft at the blue elephant's...