Sorry to hear that the combination was placed inside and not able to be retrieved at this time. This question is very common on our site and the answer can be one of two things to get it opened.
One is to contact a local locksmith but that could have your safe broken into and then not easily used again. The other option and one that is always suggested on our site is to contact Sentry directly as for a small fee can get the combination to you securely. Since the combination is a safety feature, nobody but Sentry will have this combination for your safe.
Follow the instructions listed here on this link and your combination will be sent to you quickly: