This mission easily makes the top 5 most annoying in the entire series, IMO. That's just cuz I hate the boats. Always have.
Unfortunately, there isn't anything more you can do but practice. Learn when to accelerate (when you want to go straight), when to apply the accelerator with caution (when you're turning), and when to let off of the accelerator and "steering wheel" completely (when you're landing).
Practice, practice, practice. And don't get mad!