You have to set up the corner coming out of the sewers to allign for the DS, If you are desperate you can use DS before the corner to be more on the right.

Hitting the wall on that corner is not a lot slower, but if you want a good lap no walls will be hit optimally

The rest can be done without using DS.

On reverse you dont need to use any DS at all

Only out of the sewers where you use a little bit to avoid the wall, or in the dirt to save yourself.

Otherwise you just need a good exit from the dirt and sewer section and the jump section and your lap is good.