True. It's because you get points deducted for driving in water, and for Koopa Beach 1, you absolutely HAVE to drive in water.
It bugs me, but I should probably just skip it at this point, it really doesn't seem doable.
I actually did it! You need to know that driving on dirt and sand doesn't actually hurt your score. The worst is Koopa Beach 1, where the drivable water counts down your score...
After my frustration, I needed to know how the 3 stars where calculated, so I could adapt my gameplay. So I found online RAM memory data positions where you can see your points. Upon analysing the data during a race, I notice the value of "off course" wasn't incrementing like it usually does (in Koopa Beach's water it goes up).
It bugs me, but I should probably just skip it at this point, it really doesn't seem doable.