In general the metaphors they use are not extremely well thought out, so it is pretty hard to decipher an exact meaning from them. That is mostly due to their conversation being live and unscripted but... As a native speaker, here is my interpretation:
For more context, the section of the video the speakers are discussing how they think so much of a person's action are done in response to a fear of dying. They are then listing how that fear is shown in technology.
Person A: "So much of it is driven towards the idea [...] of a kind of holy grail of immortality. You know we could upload our consciousness to some kind of cube. You know we could freeze the body and then plug it back in. Is there a way for a human being to exist on a mainframe and -"
Person B: "Or even the documenting our life or the proliferation of how many photographs everyone takes a day and what is that? A desire to say I'm here and I'm alive and -"
Person A: "And I'm holding it all. It isn't it just like slipping through my fingers. It's not a passing thing, its -"
Person B: "But it's not meaning [anything]"
In the context instead of "everything under control" (which isn't a bad guess), "holding it all" would mean "living your life." Or at least some attempt at proving to yourself and to others that you are living your life, even if it is unsuccessful.
This meaning is contrasted with what the speakers see as the reality of "it ... slipping through my fingers." This expands the meaning of the first phrase by presenting the two as opposing options: you are either holding your life, or letting it slip through you fingers.
Overall, I think the point the woman is trying to make is that people want to surround themselves with or be close to the proof that they are beings far away from death. The constant pictures people post is the same as them "holding" the evidence that they are indeed people that go on adventures, make plans with friends, etc. and because those plans keep happening (with the proof of more and more photos), they will continue to happen without any obstacles in the future.