I don't think that you can cancel bids in order to withdraw the listing. You can ask the bidders to do so, but I think that would be counter-productive.
If your terms are clearly stated in the listing - anywhere in the listing - then I would just handle the e-mails as they come in (gently!) and leave the auction as is.
You might also reconsider revealing the reserve price after a few days. Sometimes that gives the bidders hope instead of leaving them frustrated. Just a thought.
I may be wrong, but I don't think revising your listing here on Auctiva will transfer to the listing on eBay...
2purrcats