What can I do if I'm not satisfied with the highest bid on my eBay auction?

You accept it and send them the item anyway. That's the risk you take when you put an item up for bid. By offering it for sale on eBay, you agreed to accept the highest bid when the auction ended. You need to live up to your agreement.

(Next time, remember to set a reserve price, if there's a certain minimum amount you need to get.)

Per eBay, you can not cancel the auction if someone won. You are able to set a fixed price or a reserve price. A reserve price means the highest bid must be more that then the set minimum you are looking for.

It is always safer to start your item at the lowest price you would be willing to sell for; anything above that is a bonus.

How would you feel if you were waiting for a week for your bid to be rejected.