Not sleeping well the night before is completely normal and understandable, but it’s highly unlikely to affect your performance – if, of course, you focus on getting the right amount of sleep the week leading up to the race.
The most important is the night before the day before the race. The evening before the race, stay off your feet as much as possible. Rest is as important as sleep so, even if you’re not sleeping, relaxing with a book or watching some TV will do the trick.
Make sure all your race kit is ready before you hit the hay or being unorganised will only add to the stress. Use the time to go over the race in your head, focusing on the course, how you want to feel during the race, and finishing strongly in your goal time. That should help your drift of happily.