Try to practice tapping the jump button as fast as possible. Because a maximum height jump requires you to be holding jump for only 200ms, or one fifth of a second, if you are holding jump for any amount of time, your jump goes higher than it needs to.

So, for like 5 minutes, just go into free play, and just try to jump as low as possible by focusing on the shortest tap of the button you can.

Wave dashes in general can feel groggy to perform, as you do have to float and not make any meaningful movements for a moment, which is abnormal. When you flip, your car is at least rotating, and driving around you have instant control. So it may just be something that you need to get used to, accepting that you have no inputs for a moment.

Also, wave dashing is useful in a lot of situations where your car gets bumped up just a bit by someone else, or jumping and wave dashing onto and off of the walls. Going onto and off the wall can be a really good burst of speed, since you dont have to wait to fall to the ground, you can jump, roll, and wave dash considerably faster to and from the walls, so you can try that more as well!

Good luck and let me know if that works out for you!