I'm not an expert by any means, and in fact am just a neophyte, but I'd say in future to have more faith in delta. 5 delta is WAY out there, and implies about a 95% chance that AMZN wasn't going to hit 3120 by the close Friday. And as you said, it didn't. The low for the week looks to be about 3177. I ran the trade through Thinkorswim's OnDemand feature, and at the close Thursday, with AMZN at about 3177, your 3120P had a delta of only 11, which is still very low.
You started out doing what I would've done, rolling down the Call. Did you go for a certain delta there, or just 100 closer to the money or something? It looks like it might've been at about 11-delta. Given the trend of AMZN, I might've gone with a 20-delta Call there, which would've gotten you more premium of course. Or you could've rolled it down again later in the week.
And don't forget that your 5.94 credit meant that your lower break-even was actually at about 3114, not 3120, so you had some room to play with there.
I'm glad the trade worked out for you though.