Q: I was sued. I filed an answer telling the court that the amount the collection agency sued me for was wrong. I just realized that I paid even more money than I listed in my answer. What do I do now?
A: I am not sure why you would have been that specific in an answer. An answer is usually pretty general in nature. In other words, you can just check boxes in California and deny everything that they allege. In discovery, you can work out the details.
Now, you can file a motion with the court to file an amended complaint or wait until trial, if it gets that far, and ask the court to amend the answer to match the evidence.
You really should talk to an attorney about your case before you file an answer. If you file an answer without a cross complaint, you may not be able to sue the collection agency in the future.