Mechanism of enol ether formation
Based on what you have in the question, you are good up until formation of the carbocation by loss of a water leaving group. It looks like you are missing one of two things: 


The carbocation is resonance stabilized.
One of the carbon-carbon double bonds in the product is new.


The scheme below has two of the major resonance contributors to that carbocation. Perhaps one of give you some insight on how to show the formation of the second alkene.