Yes. The IRS says you must file a Form 1120-S if you elected to be an S-Corp, the election has been accepted and the election remains in effect.
Further, if you elected to be an S-Corp you can no longer file as a Schedule C disregarded entity. I’m assuming you were not a sole proprietor in this business before becoming an S-Corp or afterwards. If that were the case, you might have file both a Schedule C for the period prior to the acceptance of your S-Corp election and after you closed your S-Corp and Form 1120S for the time between.
If you are opening and closing your S-Corp in the same year, check the beginning and “final return” boxes on Form 1120S.
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