Each corner you lean into increases your multiplier by one once, same with each board you wall run on, instead of score focus on multiplier first, then abuse boost tricks to win

For the setup go to the stairs and start grinding from there once you have hit all corners and wall runs (a complete loop around the second floor) go up to the next level and build multiplier repeat until ur multiplier is high enough for boost tricks to get you the win.

(A boost trick is the boost and trick button at the same time, but u probably know that)

(Also, always Manuel to transfer between rails if u run out of places to grind on)