The sub job that has made me doubt my abilities

Here's the problem with people telling you you're good at something--you start to believe them.
And then, perhaps at some point, you're thrown into a situation that makes you doubt that you know what you're doing.
You doubt that you know anything at all.

I was warned about this sub job, but I took it anyway.
Because I need money to recoup the car repair account.
Because I believe that I'm an effective teacher.
Because I know that I try my darndest to be consistent and disciplined as well as fair and forgiving.
Because, if nothing else, I show up when I say I'll show up, and a lot of subs don't even do that.

I subbed four days this week and feel like I've aged 400 years.
The worst part of it is that with my OCD and my tendency to be self-reflective, I am internally reliving every day.
What did I do wrong?
What could I do better?
What could I do to prevent me from having to call the office repeatedly for backup with two particular classes?

Rationally, I know that subbing is not the same as being with kids full-time.
I'm at a disadvantage from the get-go.
I'm not the "real" teacher.
I know that I can do everything I'm supposed to do, but if other things beyond my control are not in place, I'm at the mercy of the situation.

Rationally, I know all these things.

Rationally, I know that a couple kids, who bucked me hard on Monday, refused to follow my instructions, and rolled their eyes so hard at me I thought they'd stick there forever, by Thursday, were sitting up front near me and attempting to do their work, even if they don't complete their work. Even if they play around.
That is progress, and progress for some students is glacier-moving slow.

I've talked vented to a handful of teachers who say they have struggled just as much with these students. Who tell me it's not me.
And rationally, I believe them.

But irrationally, I wonder if maybe I don't actually know what I thought I knew.