I’m quitting tomorrow

Just for a little context, I just barely got hired on in the pharmacy in my town a few weeks ago. I am a full time college student and trying to become a teacher. I have quickly come to realize that I cannot dedicate the time needed to be a competent technician. Honestly, another point I’d like to add is the pay only being $16/hour just doesn’t seem like it’s enough, especially when you consider the time needed to spend studying outside of work for the eventual exam before your temp certification is expired. I’m genuinely not trying to sound ungrateful for this opportunity and I definitely did not expect it to be easy, but I don’t think I can handle this on top of the rigorous school work I’m doing almost every day. Anyways, the store manager happens to be off tomorrow and I was originally planning to go in and quit in person to the store manager. But now that she is off I am almost considering just calling the assistant sm and just telling them I quit. Any advice? Thank you all, and sorry to vent, I just have anxiety and I do feel bad about wasting their time because they seem like good people. But I want to look for employment elsewhere.