You need to speak with an academic counselor, and possibly the ombudsman’s office for your school.
Schools can have subtly different standards for what constitutes “cheating.” The amount and nature of the “assistance” you gave to, and received from, other students may actually cross that line. I know that I have students who are sometimes under the impression that they can have other students correct their grammar on essays, for instance. They can’t, at our U. You need to find out exactly what lines need to have been crossed in order to find out whether what you did counts as academic dishonesty at your school.
You also need to familiarize yourself with the disciplinary process at your school. Is there an assumption of innocence, or guilt, when accused by a professor? Is there a formal hearing, peer review, or just a lone determination by a single Academic Discipline Officer?
Do not sign anything until you have those two pieces of information.