Gaining

Bad experience with cake shake

Disclaimer a bit of a messy story.

I just had a cake shake like 2 hours ago, I only had about 1/4 of what I made and within 5 minutes it all came back out. I didnt know it would be that hard having a cake shake how can I build up to it and drink as much as others do?
I do have Double cream like 600ml a day and am so far relying on that for gaining (I didnt have cream the entirety of the day building up to having a cake shake)
3 weeks