Without reading your contract, all I can do is tell you it means what it says. Unless both parties agree to change an aspect of the contract, the terms of the contract are in force.
If you requested extra time to resolve some issues, what did you offer the seller to want to grant you the time? If you allowed it to expire without a threat of rescission, what would cause a seller to extend?
Now, just because the time expired and your good faith deposit is at risk, you can still pursue your options of completing the sale, requesting some adjustments although you don't have any leverage apparently or walk away and possibly lose the deposit.
Your agent is the person you need to discuss this with. They are supposed to look out for your interests and keep you informed of your deadlines, options and strategies.
I hope things go well for you.