Unintentional Plagiarism and disclose on Grad Applications

[owlv]

Hello everyone, I got this issue to bother me a lot, and I hope I could get some advice for you guys. 
I had a biology lab course, and there were small open book quizzes posted online - Canvas -  I copy and paste from Google, which is allowed with proper citation. But I was too tired and forgot about that. The TA reported to the university, and I received University Warning and attended a mandatory academic integrity seminar. I still have A on this class, nothing on the transcript. And I have a fairly high GPA, 3.94
Years later, our university has something called non-disclosure. Basically, the student conduct office will not disclose the misconduct to any third parties. They approved mine because my misconduct was fairly small. But the officer who approved it said I still should be completely honest about the situation. 
In the college application, I did check Yes and wrote a letter to explain the situation. But it still worries me, how bad this plagiarism will affect my college application? 
I believe I am a very competitive candidate with high GPA and several internship/research. And with non-disclosure, I could say No, but I still say Yes because I want to be completely honest, and I don't want to worry about it in the future. 
Thank you for any advice, comments, thoughts on my issue.