was accused of plagiarism

Me and the 14 other students (thats 1/4 of the entire class) who were accused of plagiarism in my class went to discuss our assignment with our prof individually. I tried arguing about where i found the information in the text but he didnt want to hear any of it. Luckily, he was kind enough to give us a warning, however if he catches us plagiarizing again, we will receive two notes of misconduct on our record. That being said, i dont know what to do because i feel like i have a target on my back because if he believes i plagiarized the first time (even tho i didnt mean too intentionally) what will make him think i didnt do it again? Should i just drop the course? Because id rather retake another level 300 course another semester with a different prof or will that make me look even more suspicious? If i drop the course can he still put a code of misconduct on my record? I know i should go to student advocacy, but what will i say since its not an official case of plagiarism?