Examples:
“Really?” I said, widening my eyes.
"What?" My eyes lifted and I raised my brows in shock.
I think this reads strange because the narrator can't see his or her own face (or wasn't able to back then).
So I tend to write this instead:
I was taken aback. “Really?”
"What?" I said, startled.
But I don't know, maybe I'm wrong and authors write stuff like the first examples all the time?
Although the narrator can't see his own face, he'd still feel his face moving, so I don't think that's the reason it feels strange. It sounds strange to me because the actions sound intentional. Facial expressions are generally involuntary. I don't raise my eyebrows in surprise -- they rather do it of their own accord. Your writing could reflect this:
"Really?" I gasped, eyes wide.
"What?" My eyebrows flew up in amazement.
Your second examples also make sense, because we have access to the narrator's emotional state in first person POV.
"Really?" I was shocked.
"What?" I couldn't believe what I was hearing.
It depends on what kind of effect you want.
As @kitzfox says, there are times when you would know what your face must look like, and it would be reasonable for a narrator to say so.
I stared wide-eyed.
Sometimes you would reasonably guess.
"Bob is the smartest man here", my girlfriend announced to the room.
I could feel myself reddening with embarrassment.
But other times it would be distinctly odd.
For example:
I had a tired look on my face.
Umm, probably not. You might say "I was tired", but you are unlikely to describe yourself as looking tired.
If it's somehow important to describe how a first-person narrator looks, to make it sound natural you could either have someone else tell him how he looks, or provide some way that he sees himself.
I didn't realize how tired I must be until Sally said, "Wow, you look exhausted."
"Does it really show?" I asked.
Or
As I walked passed the mirror, I glanced at it and saw my own reflection. Wow, I looked tired!
When I think about myself, I only think something like I raise my eyebrow when I do it consciously, that is, when I "play" some emotion and "make a face".
In all other situations, when I face reflects my emotions, I am usually not aware of this, and in fact I have often been surprised when people told me that I look this or that way, because I was quite sure I was hiding that feeling.
So when I read a first person narrative, I expect to read about what a person thinks, what they feel, and what they experience, but not how their face moves or what it looks like.
Sometimes a person may think about what they look like from the outside, but this is rare and usually made explicit.
[Someone does something that takes my protagonist aback.] Surprise made me hesitate, then slowly a deep dislike welled up in me, replacing the attraction I had felt until then. "Really," I said, as [whoever] slowly changed in my eyes, like a shapeshifter, from desirable to appalling, [contd.]
and I felt I suddenly didn't want to hear another word from her ugly mouth. Maybe not in those exact words, but you get the idea: in first person narrative explore the emotions of your protagonist in the same detail you would explore the outside appearance of him in third person.
From my PoV, depends on the style of writing, example (sorry if it doesn't sound as great as in my mind, not english native):
The street lights were flickering. From my seat in Builders Street bus stop i was able to see a shadow move between two piles of boxes. I raised an eyebrow and shouted "Hey, is someone there?", but i got no response. The lights flickered again, and i felt a cold chill on my spine. There was another shadow besides mine...
