Yes, you can still use TurboTax to prepare and file your 2018 return. If you are getting a refund there is no penalty for filing after the April 15 deadline. If you owe tax due, then get it accomplished as soon as you can, since your penalties and interest have begun.
Interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.