Hi, skamocore. I think you've got yourself some troubles that don't have to do with pixels and c64 resolutions but with how to construct a human face.
Here's a step by step edit I did of your piece, but I don't know how helpful it is given that it uses foreknowledge you might not have.
First I removed the face completely as I was going to start from structure. Then I pulled the face foreward and shaped the neck. This is a very common beginner human anatomy problem, propping the face on what amounts to a cylinder or pyramid completely in the middle. But the neck is a spine, carotyd and other life support and a lot of muscle (a LOT of muscle) to keep it not only propped but moving in every direction it needs to go. Seriously, look at pictures of cute girls with scrawny little necks, you'd think there's no muscle there, but look at them turn their heads to the side and check out how much the tendons show. Necks are important.
Then I put on the facial characteristics according to a few simple guidelines I drew. I can't really help you internalize this step because it has nothing to do with pixel art, it has to do with studying facial anatomy as a thing in itself. I referenced your shepard 2 picture to get some likeness but really it wasn't much my priority.
Then I put on some basic light shading according to same reference so it's not that bare, I halved the image and then multiplied it by two to get it all back to being widepixelled and did a minimum amount of cleanup just so it didn't bug me and posted the edit here as it's not my own art to finish any more than that. Hope it's helpful in some degree.
