Nope - you didn't make a mistake. You will feel like you did for the next few weeks though. What you did do was embark on an incredible difficult journey, which is going to be both terrible and absolutely amazing. When you come out the other side in 6, 12, 18 months or whenever you'll look back on it and it'll be one of the best decisions you ever made in your life.
Focus on the day to day right now. Follow the plan as closely as you can, keep on top of the pain, call the DR if something isn't right. It took me weeks to get to the liquid goal and my calories were like ~300 per day for the first month, it got much easier after that. Once you start seeing weight loss (a few weeks) it'll be more motivating. For now keep busy, sip constantly (try watering your shakes down) and try to walk a lot gently as that helps with the pain.