You can end an auction early by going to your active sales list and clicking on the drop down menu to the right of the item and choose "End listing" and follow the prompts. This is possible as long as no bids have been made.
If bids have been placed, it must have more than 12 hours to go till the end, and you need to cancel all bids first.
Some may be upset if they are watching with intentions to bid, and you may lose future buyers, but until it is sold it is yours to do with as you please.
