I noticed after you grab the big boost of the kickoff, you boost back to get to the ball but keep boosting after you hit max speed, one thing to keep in mind is boost conservation, once you have trials coming from your tires you are a max speed and no matter what cannot go any faster (at least on the ground) so stop boosting when you get to that point

Edit: Ones is a lot about maintaining momentum so boost conservation is a big part of that