It almost happened to me once, I was lucky that the deadline was flexible, unless I wouldn't have made it ? It happened when I had just started to get a kind of steady workflow, so I was too eager to take on as many projects as possible (fearing dry spells). Needless to say, this taught me to never to overdo it and that sometimes you need to say 'no'. Quality is obviously better than quantity, plus you might lose a project if you turn it down, but earn clients in the long run by always taking the time to do an excellent job.