My teacher falsely accused me for something i didn’t do and he wrote me up. idk what to do?

I knew it from the beginning of the school year, my physics teacher had some bad vibe. He always had something to say about me, negative things. But today, I’ve had enough.

We have two teachers in our physics class and I asked Mr. Thompson if I could use the bathroom and he said yes. By the time I got to the door, Mr. McFlar asked "where are you going?" and I said "I’m going to the bathroom" and he said "No your not, your going to see Laura. Get back in" and I responded "Uhm, no I’m not. I really have to go whatever."

So I went to the bathroom and when I got out of the bathroom, I saw Laura (she’s a guidance aid. Guidance Aid – student who helps school environment by lending counselors a hand by distributing hall passes for certain individual pupils for scheduled appointments) and she asked me if I was going to be on the bus today and I said yes. Then Mr. McFlar saw me talking to Laura through the window on the door and started yelling "IF YOU LIE TO ME AGAIN, I’M WRITING YOU UP." Okay, me and Laura wasn’t going to have a long conversation since she had to give out hall passes and I have to go back to class plus I actually did went to the bathroom so last time I checked, I didn’t lie.

When I got back to class, Mr. McFlar wrote me up. So it looks like he was the one who lied because Laura and I remember him saying "IF YOU EVER LIE TO ME AGAIN (<–keyword), I’M WRITING YOU UP".

1) I did not lie to him. I actually needed to go to the bathroom.
2) I never lied to him even once.
3) He was the one who lied about the "again" part.

He handed me the detention slip and the reason stated: LYING ABOUT GOING TO BATHROOM. How is that even possible when he was in class teaching or maybe he’s not even doing his job and he’s just too busy watching me.

I’m going to school for me and only for me and this teacher is blocking my full potential of earning a successful education and it is simply unacceptable.

typically one detention slip is a non issue, but if you accumulate several, that can become a hindrance to your education.