I have had to do this twice, (dangers of toddlers' on lap while at computer one time)
An example, bid amount was too high 1034. instead of 103.40, I immediately retracted bid then attempted to rebid,I was denied by the ebay software. A question to ebay came up with no useful information in reply.
One other time same result.
Chalk it up to the electronic frontier.
John Jorgensen
Palos Verdes Ca