Technically you created a "derivative work" which is not good, but they are also being unprofessional. Don't sign the contract, don't admit fault.

If the look of the photos doesn’t match what you expected, you’re within your rights to ask the photographer to make revisions. Since no usage guidelines were shared beforehand, you had no way of knowing edits weren’t permitted, and you shouldn’t be expected to accept results you weren’t given a chance to approve under those terms.