The Online version automatically saves after each page of entry & will save again when you sign out. You can just sign out and come back when you have all your information.
There also may be some forms in your return that are not finalized for filing.
See the following for a list of forms & when they will be available for Online, Windows, & Mac:
IRS Forms Availability Table for TurboTax Individual (Personal) Tax Products
https://ttlc.intuit.com/replies/3319876
