There is nothing wrong with "Maybe I was mistaken."
It does seem odd because Mistaken is more formal than maybe.
I think it would be more congruent to say "Perhaps I was mistaken." 

Something less formal with the same meaning:
"I could be wrong."

What is another way to put "mistaken about what one saw"?
Is potential energy and "work done" the same thing?

If they are not one and the same thing then why is potential energy always associated with "work done"?

Could you explain me with some examples?
