Started college-level classical voice lessons and suddenly I feel like I don’t know how to sing 😭 Advice?

So I just started one-on-one college-level vocal training and I’m coming into this with basically NO classical training. I’ve been singing for a while and walked into my first lesson thinking okay, I can sing, I have a decent range, I know my voice pretty well, etc.
Then my professor had me literally go “AH! AH! AH!” over and over again and apparently I could not say “ah” correctly to save my life 😭
Eventually I finally got what he wanted, and it’s such a specific feeling. It feels VERY forward/high, almost like the sound is hitting around my hard palate, and it’s surprisingly loud and precise. It’s not really yelling, but it’s a much more direct, projected sound than I’m used to. Once I finally found it he was basically like YES, THAT.
The weird part is that when I try to maintain that same coordination through scales, I feel like I suddenly have way less range than I normally do. I’m assuming that’s because I’m learning a completely different technique and I shouldn’t be trying to force my normal range out of a brand-new coordination, but it definitely humbled me lol.
Now I also have to start learning Italian classical/art song repertoire, which is completely new territory for me. Most of my singing background is contemporary — pop, rock, belting, etc. — so I genuinely don’t know what I’m supposed to be listening or feeling for when I sing classically.
For classical singers/teachers: what actually changes when you go from contemporary singing to a healthy classical sound? What should I focus on most in the beginning — vowels, breath support, resonance, soft palate, placement, vibrato, diction, registration, something else?
And when it comes to Italian, is there anything you wish someone had told you when you first started singing it?
I’m also curious about the timeline. I have a performance in December. Obviously I’m not expecting to become an opera singer in three months lol, but if I’m practicing consistently and working with my instructor every week, is that enough time to get comfortable enough with a few pieces to perform them convincingly?
Basically I walked into my first lesson like “yeah I can sing :)” and walked out realizing I apparently need to relearn the letter A. 😂
Any advice for a contemporary singer entering classical training for the first time would be VERY appreciated.