Step 6 says to use 2/3 of the sauce to saute with sausage, then pasta and peas. What are we supposed to do with the remaining 1/3 of the sauce? Do...

It's Italian food so it isn't fussy. I would add all the sauce and call it a day. That's just me. I get crazy like that. Seriously, if you don't want extra sauce lying around you could reduce it more so it thickens and then omit the 1/2 cup pasta water which is meant to add starch to the sauce which thickens it as well. At least that is what I would do.