If he failed you due to plagiarized work, there are two concerns at play:
1- there are larger, school-wide consequences to plagiarizing
2- if you do not understand how to properly cite information you’re using, or how to take good notes that don’t plagiarize unintentionally (by copying phrases that may be from a textbook or a website into your writing), your future college work will be impacted
Both of these concerns will require you to talk to the professor and understand the type of plagiarism he found in your work. However, I would reframe what’s happening- professors don’t give grades or ruin GPAs; they record the grade you earn. You did not think that you were plagiarizing, but it is possible because you are new in college. Could the two of you meet when school starts to discuss so that you can learn for the future? (because, again, you have much bigger problems further down than this 1 D if you are unintentionally plagairizing).