what i am doing wrong?

There's never anything completely "wrong", just point that we can improve on! There's a lot of potential in an absolute beginner.

What stands out first is the proportions and positions of the facial features. I do the same thing, where I focus on redndering one feature at a time, forgetting about the bigger picture 'til the end. I would recommend sketching the general size and shape of those features before going into smaller details. For example, from the bridge of the nose to the edge of the nostril to the tip takes a triangular shape. Find that first before scultping the slope or the nostrils.

Another tip is to look at pictures and tutorials learns some rules of thumb. For example, in profile the length of the earlobe is almost the same as the length if you drew a line from the bridge of the nose straight down to the base above the lip.

I like how you followed the fall of the hair when rendering the head. I would recommend looking into using the wide side of the pencil to fill in large areas instead of using small strokes.

As a tip on technique, I would advise using a light hand at first to sketch out a base, and then use a darker pencil when you want to commit, instead of using an eraser over and over again.

I'm sorry of this is a bit long-winded or complicated. Like I said, there's already a lot of potential in this, and I wish you good luck!

Reiterating other comments, your line weights are all very heavy, try using some light lines as you are still working out the geometry.

Move to darker lines once you are finalizing the form. Very light lines can give your drawing subtlety, line weight should "whisper" to your viewer and not "scream."