Plus a $5 bonus isn't as big an oversight (in my opinion) as a larger bonus. However, I think you were totally within your rights to cancel the shops. You and the MSC agreed to have the shop performed for a certain amount, the MSC noted that there was an error in their offer, apologized, and revised the amount. You were no longer interested. It all sounds very cordial. Maybe you'll get another chance at the bonus in a few days if they haven't been scooped up.
Shopper in California's Bay Area