When your employer forced you to stay he made a business decision that had a cost and a reward. He (at least should have) weighed the cost vs. reward and assuming he did, determined that it was more beneficial (either financially or otherwise) to have you remain on the ground two more days. At that point, your employer is on the hook for 100% of the cost of doing business to get the reward.

However, once you offered up your miles, you essentially stated that you had a way to reduce the cost of doing business. Your employer probably assessed your offer as a way to REMOVE the cost of doing business not reduce it. Regardless of which way he viewed your offer, you cannot assume you will get the full $1K because then there would have been no reason to accept your offer.

Now that the transaction has taken place, you are in a weakened negotiating position. You should request some form of compensation but, at this point, you should consider yourself lucky to get pennies on the dollar if cash at all. My guess is you will be offered extra time off, a shiny new stapler, and a lifetime supply of paper clips.

Sorry, chalk it up to lessons learned.