You probably developed a wants and needs list before purchasing the house. Find it and review your notes.
Does the home include the most important things on the list?
What qualities made the house you chose stand out from the others you looked at?
Did you find many houses that met your needs or was this one a rarity?
If you can back out of the contract, is it realistic to think you will find a house that's "better?"
What was special about the house just a few days ago and how has it changed--really changed?
Analyzing the facts that lead you to the home will help you sort out your feelings about the contract. Was it truly a poor choice or would you be nervous moving forward on any house?