High School Student In Need Of Help

I am a high school horn player, and I'm having a bit of a problem and I am not quite sure how to fix it. Im struggling with a portion of my range from about first line E down to third ledger line F. That portion of my range is definitely more weak than the rest of my range in the sense that I cannot play it forte/fortissimo or as well as the rest if my range. It feels like my lips are not able to buzz those notes like they can in the low range and high range. Thank you, I tried to make the most sense possible, sorry.

In the high range just the center of the lips vibrate. In the low range the whole lip vibrates in the mouthpiece. Philip Farkas in his classic The Art of French Horn Playing (you do have it don't you?) suggests to blast those notes to get the lips accustomed to them. Play them as loud as you can. Works for me. Of course this is just weight lifting. You don't play that way normally.
Herb

Its difficult to blast the notes because, for example, when I play first ledger line C, after a certain volume, I lose control of the note. So should I try to just play it as loud as I can, or does it need to be loud? Thank you.

Play it as loud as you can, walking the line of losing control Do it with air, not the lips. I do that as part of my warmup routine.

Don't let your embouchure go floppy. Anchor the corners of your mouth firmly and keep a bit of tension in your top lip. Let your bottom lip vibrate freely. Don't play too loud - you are not ready to blast low notes; play as loud as you can without going out of control. Play scales down into the low register.

Try experimenting with opening the teeth and/or bringing the jaw out a bit. You will need to be more open for loud. A low C at FF is different than a low C at pp. Hope that helps. If that doesn't work, your tongue may be in the way (too high).