How to beat Wedding Cake in Sleeping Dogs.

Beating a wedding cake is illegal it should be eaten. Yeah, odd title just had to make a funny comment about it. Anyway! Onto my question....

I have looked everywhere in guides and on the internet for a detailed explination of how to hijack the wedding cake truck in sleeping dogs.. every time I jump on the truck I am hanging on and when I press the right mouse button like it says.. I fall off and end up rolling down the street then the game over message comes up with "Restart Mission"...so I tried again and held the button this time while trying to move. then I didn't use it at all..pretty much tried every single way. So, How do i get in the drivers seat of the truck without falling off?

and Trust me. I've tried to look on Google and through walkthroughs and all they say is Complete hijacking it then move onto next chapter etc.. idk what I am doing wrong. So, any help from players who have beaten this level would be appreciated greatly!

Thanks!

TL;DR: Can't hijack sleeping dogs wedding cake truck mission. Keep falling. How to beat?