I'm not sure I can go

[Topstudent]

Four friends are out drinking beer. Friend #1 suddenly gets the idea that they should go on a cross country road trip the next day. Friend #2 and #3 think it's the best idea ever. The three of them start planning the trip, when Friend #4 breaks in...

Friend #4: I don't know, guys... "I'm not sure I can go.

Friend #1: What?

Friend #2: Why not?

Friend #3: What the hell are you talking about?

Question:

Is "I'm not sure I can go" perfectly natural here?

 

[tedmc]

Yes. You could put in "if/whether" before "I".