There's simply not enough information to soundly conclude that God must necessarily exist because you likened the Universe to a watch. Plausible? Sure. Sound? No. That's about as clear as it gets.
I'm not even sure it's plausible. Invoking a god because of a lack of either imagination or knowledge (or both) is the ultimate deus ex machina - an difficult problem solved by a being that can solve any problem.
To me this is just intellectual laziness. It's just too easy to say "well I don't understand, so it must be caused by a god of some sort".
difficult != impossible