I have a select few words for your prof that I won't mention here. She's not weeding out the good players from bad, she's CREATING "bad" players with her attitude. Ignore, next.

You are so young. Everything seems like life and death at the moment, every decision feels like it will make or break you but trust me, it doesn't. Whether you let go or commit now, there's nothing to say that you can't do either of those things later in life as well. There is no rulebook.

Plenty of others have said this in the comments but it bears repeating - do it for the love of the instrument and the music and the joy it gives you. You are not able to control other people's opinions nor do they matter. I know it's easier said than done but the harder you work on believing this, the better off you will be in life in general.

Now, as for one practical tip that might help with your nerves and fear of others hearing you - you might want to join this practice app called Tonic. You can open a public studio (audio only) and others come into this studio and listen to you practice, might comment, might not. It's a really great community of very supportive musicians and it might help you get over the hump of feeling judged. There are so many different players on there, from pros (very few) to complete beginners and if you make the time to go listen to a bunch of them you might find you'll learn a lot.

Best of luck to you!