Decide major product for first order elimination reaction
The product that you have drawn is very unlikely to be the major product of a mixed aldol condensation. The actual major product in said reaction would be (assuming I get the substrates right) would be as follows:



However, your question is a valid one if we take this out of consideration. Now, If we consider just the elimination reaction and your reaction conditions, your mechanism is correct. However, if this reaction were to take place via E2, the rate determining step would be that of the removal of the hydrogen and this would mean that the product formed would be (c). In case of E1, (b) would be the major product since the rate determining step is that of the formation of the carbocation.