No, there is a special rule to protect people in your circumstance.  If the Marketplace found you were eligible for premium tax credits at the time you enrolled (because your best estimate at that time was that your annual income would be at least 100% of the federal poverty level), and if your income later fell below the poverty level, you are still eligible for the tax credits you received last year.  You will not be required to repay the premium tax credit when you file your tax return.  To benefit from this special rule, advanced premium tax credits must have been authorized and paid for one month or more during the year.