Fear is one of the great motivators. Don't worry about how you will feel, deal with that if it happens...IF it does. You should know though that most of the great successes came after people failed a number of times before. Succeeding in business is for the most part like succeeding at anything else. Before Neil Armstrong walked on the moon, years and years of failures preceeded that success. NASA didn't focus on the failures...they learned a little more from each one until they could finally cajole an astronaut to sitting on top of one.

Ideally, you've done a good job of researching and developing your businessplan and will work as hard as you can at your new venture and learn quickly enough from errors to recover...if this isn't the case and it doesn't fly...you can look back and say...I did my best, I have nothing to be ashamed of.
Good luck,
Denny