My take on the ending
I'm not sure if this is right or wrong, but here is what I got on the ending.
David goes back in time after Jesse goes missing, back to his 7th birthday party. He sees his father and talks to him, telling him to say goodbye to his son. His dad leaves, and he destroys certain aspects of the time traveling machine. He purposefully leaves the camera behind, the camera that has documented all of his adventures (as stated earlier in the film). He then stays and lets that self die.
Then his 7 year old self grows up exactly as intended to be. The only difference would be the camera that was left in the room, which possesses all the adventures (including the mistakes) that he previously made. Now that he knows what to do, he can "change the world".