When a person is both IN CUSTODY and BEING QUESTIONED, the police must read the person their Miranda rights. If the police do not read the person those rights, then anything the person says cannot be used in court against that person.

In your scenario, you are in jail so you are IN CUSTODY, but there is a second prong. If the police did not question you, but you made statements on your own, those statements could still be used against you.

Also, consider this scenario, you are IN CUSTODY and you are QUESTIONED and you have not been read you Miranda warning, so anything you say cannot be used against you in court. However, there is so much other overwhelming evidence against you (like fingerprints and an eyewitness) that you are convicted on the other evidence even without your statements.

So the answer to your question, is yes. Under some circumstances you can be found guilty, convicted and sentenced even if you were never read your Miranda warnings.