Yous shouldn't file your return yet, but you can get a headstart on preparing it. Just be sure to click Sign Out in the lower left corner of your screen when you are ready to put your information on hold. Once you have the rest of your tax documents, you can sign in to your account, click Take me to my return, then click Pick up where I left off. (Click the screenshots below for reference.)
Remember, do not file your return until you have all of your tax forms. If you do so, you'll have to prepare an amended return and mail it to the IRS. The IRS takes 12-16 weeks to process an amended return.