From fan-made transcripts:
Bucky Barnes: What's gonna happen to your friends?
Steve Rogers: Whatever it is... I'll deal with it.
Bucky Barnes: I don't know if I'm worth all this, Steve.
Steve Rogers: What you did all those years...It wasn't you. You didn't have a choice.
Bucky Barnes: I know. But I did it.
So the line reads: "I don't know if I'm worth all this, Steve."
Steve Rogers is in the middle of risking his own life to protect Bucky from the other Avengers and Black Panther. Bucky is referring to everything that Steve is doing when Bucky says "this".
So what Bucky really means is something like:
"I don't know if I am worth all of the effort and risks you are taking just to protect me, because I did many bad things and I don't deserve your help."
What Steve says next shows that Steve understands all of that even though Bucky only says "all this".