If it’s before December 15, you should return to the marketplace as soon as possible, review and update your account information, and shop for a plan that better suits your financial and medical needs. Open enrollment is much shorter in most marketplaces, from November 1 to December 15, and there is only one deadline to enroll and/or to make plan changes. (82 Fed. Reg. 18346, April. 18, 2017).