I really don't know a great deal about your movement, but I've heard of it. That makes me qualified to offer the outsider's perspective on why it's not as effective as it could be.
First, the name doesn't catch my interest at all, although it is a memorable name. Seven77? I have no clue what it's about, and absolutely Zero00 desire to find out. I'd suggest that you revise the name to give at least a reference as to what it's about - and one that people outside of STEEM will understand as well.
Second, while I've heard people mention something about doing 7 push-ups, I don't immediately connect that to your movement. 7 is a pretty common number after all, so I figured this was just the latest iteration of planking, or the ice bucket challenge, or some other silly Internet fad that I have no interest in. Why 7? I checked out one of your posts about it and you mention that STEEM should be worth more than $7.77... That seems to be a rather arbitrary figure. Again, by revising the name the entire thing could make more sense and be appealing to a wider audience
Third, how do pushups relate to STEEM anyway? So many of us are keyboard warriors. I applaud your effort to encourage movement, but I simply can't see the average Twitter fan saying, "Man, I really want to join STEEM so I can do pushups for 77 days!
And finally, the length of your challenge is simply unrealistic for most people. Even Lent is only 40 days. Asking people to commit to an unknown platform for 77 days is setting folks up for failure. You'll have a few that make it, but the majority will likely fall off within the first 2 weeks. Perhaps consider a series of weekly challenges designed to bring the Twitterverse in closer contact with the Steemosphere.
Just my two cents.
And thanks for hosting a contest asking only for criticism. That's refreshing.