The subliminal force was a little bit too obvious, so it didn't work for me. It didn't seem like it was natural for you, it seemed like you were doing the motions too purposefully. I caught on from when you made the diamond shape with your hands. I see how it could work on someone, though, and overall it's a clever idea.
Also, I feel it may be more effective to begin the subliminal force before you tell the person that you want them to envision a card. I know you did the three-finger motion before, but the rest of the force was after the person knew that they had to think of a card, thus they may have had one in mind before your force worked.
This is the sort of thing that requires a great deal of thought and practice as well as being willing to accept that you may not have the right style for doing this sort of force. Not everyone can get away with psych forces and too, there are those that can make certain one's hit every time and miss on some of the more common, like the Trine & Circle.
Pre-conditioning the mark well in advance is always the best way to do it. Colin McCleod has a wonderful technique for flashing an image or information to the participant. It's kind of an Instant Stooge type think but when handled properly the subject only thinks they saw something because the details are literally flashed in a split second and then everything appears to me normal (unfortunately I can't find the link to the download). Another method common to card work is to keep flashing the bottom card to one particular spectator (insuring you have the same card in place and even moving about in location if you are good at such control while doing other routines). You don't need to be overt, less is best but flash them the card you want them to name and nine times out of ten, they will name it. . . this is also done with a Waterfall force
Do some experimenting and learn how to read the people you use, some personalities just don't fall for the subtle (and not so subtle) suggestions.