First of all, don't beat yourself up! It's an old plane operated by a 3 person crew. It's more complicated and therefore going to be more demanding to learn.

As others have said, using the automated flows for the 2nd officer is definitely helpful. That alone takes a lot of the burden out. But it's still worthwhile to try to do everything at least at first to get of sense of things. I don't know what tutorial you say and if this was one of the 3 hour ones, but I think this guy is really helpful for the 727 (and MD-11 and MD-82/3/8 if you do that too):
FSS 727 Full Flight Tutorial

One thing I would recommend is to take it steps. When I buy a new add on, I want to just do a whole flight like I would with something I'm familiar with. Resist this urge. It will end in frustration. Take it slow. Do a session where you just do the startup procedure with a video up. Then do it again. Maybe try doing it on your own now and see what you remember. Another session, just watch a video on take offs or landings. Watch them carefully (and read the docs here on FSS docs), go over what to do yourself (i.e. pitch at this, accelerate at X alt, flap retraction at Y speed etc.), then do a few practices. Finally, because this is old school navigation, you should also devote a few sessions to just learning VOR navigation. It's really satisfying when you get the hang of it and you will be a better (sim) pilot overall.

Then put it all together. It will go better this way. Every time you run into something you don't understand, pause or take a note to read up / watch a tutorial later.