Unfortunately these people who answer questions from out of state, don't know Colorado's contract and as such are not the best people to answer. The appraisal contingency is only valid until the date agreed upon. If the seller won't extend the deadline, you need to hope the appraisal comes in at value. If it does, no harm, no foul. If it doesn't come in at value, you have two choices: First would be to come up with difference in cash, and continue as planned. Or, second walk away and probably lose your earnest money deposit.
If this was truly an error on the part of your lender, I would ask them to pay you for any earnest money loss. Please feel free to contact me with any questions!