I’ve taken the canon test, which say that I am Prospit, and according to my MBTI, I am Prospit, but I don’t feel like a Prospit dreamer? How can I tell for sure if I’m a Prospit or Derse dreamer?

You really can’t, Hussie’s own description about the Prospit/Derse duality takes into account every possible case from ‘tendencies you need to overcome’ to ‘what’s more fitting’, it’s pretty dubious. If you feel more Derse, go Derse really.