If you're doing this correctly you should land on a page titled ""Stock Option Lot Summary." On that page is a button titled "Add Another Lot". You keep adding another lot until you're done. If instead of clicking on "Add Another Lot" on that page you click "done" then you're placed on a page titled "Add Another Lot" showing how many shares are unaccounted for in your sale and asking "Do you want to enter another lot?"
If you're not seeing that then I'd guess you're in the wrong place. Delete and start over.
