How Do I Tell My PI I Want Out Of His Group

Hi Everyone, Right after I graduated with my Bachelors in Chemical Engineering, I directly entered into grad school, starting a Master's degree in the same university I did my undergraduate studies at. I (22F) am now completing the first year of my M.Sc program.

The summer after I graduated, I was visiting different professors to ask if I could intern in their labs for the summer time. One professor got back to me and told me to just start a Masters program and join his group in the fall. He didn't bother looking at my grades, or my recommendation letters, he didn't try assessing if I was ready for grad school (I wasn't). The program is free.

He was working on an artificial heart pump, and at the time I was vaguely interested in biomedical engineering. I said yes to his offer because I had no plan and I thought it was a good idea (not a good idea).

This professors main focus and area of expertise is mechanics, not necessarily biomedical device engineering/design. So that project he had focused on the pumping mechanism. To be clear he is the director of the mechanical engineering department at my university.

The first semester I chose to audit some classes because I lived very far from university and had personal things going on. The professor attributed my absence to me being a bad student. He would often make comments on my lack of presence (he expects grad students to be at the lab like a 9-5, which i learned eventually is normal). PI knew about my personal circumstances but was not accommodating. In the second semester (now), I improved slightly, would send in my weekly research reports, but focused more on my classes than the research because I didn't like the topic of my research.

Fast forward to now, I am taking three courses. I realized through them that I would rather pursue something with more science, more biology because I know more about those topics. I thought I could get into automation engineering, but the prof did not help me learn what knowledge is needed, what courses I should be doing, and I only wish he did because when I joined his group, I was 21 at the time and I did not have my passion/area of interest developed. I took on the insulin pump as my foundation to what could be my thesis, but I have no joy learning about pumping mechanisms. Also the lab group environment was the worst, no one made an effort to speak to me, I made efforts to interact with them but they like to keep to themselves, im pretty sure its because I am not a man. And I think they view me as less than because my background is not mech engineering (all of them are).

Right now (22), I am scared, because I do know in my heart that I do not want to stay in his group but that also means I need to find another one to join (which already sounds difficult). I know I want to leave because I generally hate being in that lab and when I would I feel so unhappy. And I havent even started the work on my thesis. I learned alot from my experience in the lab, I learned that I do not want to stay there. I learned that my prof is an expert, but not an expert enough to guide a beginner like me into a field I dont have any background in. My friend in the lab says to stick it out and make it work because other labs wont be better. But I disagree, and I feel like the experience should not be this bad.

Ive been feeling this way for months but I could not muster the courage to make a decision and I was trying to make it work, so my PI has no idea, he probably thinks Im just being a bad student, but it feels like Im making a huge life decision.

I havent been at the lab for two weeks, and I need to tell my PI whats going on, how should i go about this? Grad school is difficult and I could use some advice.