I am so sorry that this is not working out to be the Paris trip of your dreams. You sound so frustrated. You still have a little time to get some weight off and you still have time to work toward your walking. Make a plan, stick to the plan. Don't just say that today is the day that I get it together tell yourself exactly what you are going to do today. Even if you are not perfect you will have a plan and at least you will feel better about yourself and not so frustrated. Maybe.

Just do what you can when you get there to have the best trip ever. There are plenty of ways to get around the city other than walking. There are still ways to have a blast. Don't let what you didn't do in the past influence the fun you have in the future.