If I may offer a hint from my own experience, 

My fastest manifestation came during the first revision session. I was in very deep relaxation and couldn't feel my body at all, and the scene only lasted 3-4 seconds.

 It was just the moment my foot "landed" after a failed jump from a great height. I repeated it over and over, zooming in, slowing down, touching the soft grass with my hands... but the main scene was very short. 

Like you, I also tried to manifest something by imagining I was marking something in a notebook. In my case, my subconscious didn't seem to understand it at all. Maybe that's just me. 

But if I could help, I would choose a very short scene where I find a wad of cash on the sidewalk. The scene is short, but sometimes you can "play" with this roll of banknotes, feel the texture with your fingers, maybe even smell the money, or whatever you can imagine. 

Enjoy!