Why am I not making any progress with my social skills?

So here I am asking for advice again. I (F21) am an awkward introvert with low social battery and have currently no other wish than acquire stronger social skills and improve as a human being overall.

So a few months ago I moved to a new city and decided to search for a job where I would be forced to interact a lot with people, as I heard that practice and exposure is the best way to make progress.
I finally got a job in a popular bakery/café, and me who wanted to be challenged, I got way more than I asked for. I have daily intensive contact with colleagues and thousand of clients. There are very often changes in the staff so I am meeting new people regularly, making tons of small talk, having to appear bubbly and positive and be energetic for 8 hours a day. You could call that introvert hell. But I’m putting myself through it because I won’t get such intense practice anywhere else.

But even with all that, after 4 months of working in these conditions, I feel like my social skills haven’t evolved a bit. I still feel stressed at the idea to interact with my colleagues on the way to work, even tho I know them, I still struggle to come up with anything to talk about during calmer periods, I still stumble over my words and am slow to come up with answers to playful jokes. I still have difficulties to have more extended interactions with clients than just the regular « hello » « anything else?» « have a nice day ».

I thought this experience would make me more confident and secure but it has been all the contrary. I get home frustrated, sad and beating myself up for not having been able to do better.

What am I doing wrong? I have the feeling that I will just stay the same my whole life sometimes.