I have added some debt accounts, but the amounts it's wanting me to pay are very high.
It sounds like you either have your monthly budget set too high *or* you are joining mid way through a billing cycle and you have already paid some of your debt accounts for the month. Undebt.it will try and use all of your budget each month to pay down debt and if you have just created an account, the site doesn't know that you've already made payments. The best way to fix this is to record the payments you have made in the debt details page for each account. Just make sure you choose the current billing month when entering the payment amounts. As you record your payments, you will see the numbers change in the Payments Made box on the status bar across the top of the screen. Once all of your payments are recorded, your payment plan will be accurate. If the numbers are really off, check the Account List page for typo's on the interest rate or minimum payment (missing decimal point, etc).
Here's a blog post that goes over the issue in more detail.