I'm in the same position as you. I'm entering senior year of high school. I've been playing the trumpet since 5th grade.
I was told I had a near perfect embouchure by a super teacher in the area so I haven't changed my embouchure but I've made some adjustments... Those adjustments like curling in the lip just a little bit. That means that I'm really having to deal with frustrating change.
I've had nights where I thought of exactly the same things you were thinking. "How am I going to survive in this trumpet thing? What's it worth?" because I couldn't play for squat. I've had some real real high moments before and I'm floating on those (moments like singing my heart out at a huge huge Messiah concert as one of the two trumpets, floating on top of an orchestra with American in Paris solo, just... good times when I wasn't worrying so much).
My band director who is just a real mentor of me tells me not to worry so much. She says she hears improvements in my tone every time she's heard me this summer. (And HAHA she is not the usual teacher that says good things for your sake... She's known as "THE B" to a lot of the students that are really bad with their instruments... but I mean... she was a college professor, and... I guess she's trying to help).
Anyways. KEEP IT UP. My "completely relaxed & free" range is to that E on the top space. Just like yours as you say. Anything higher requires me to apply a little pressure or do something that's not relaxed & free.
But I'm keeping up with patience and I can hear some change.
Remember, there are no shortcuts with music.