Scared I have accidentally committed plagiarism?

I am an undergraduate student at university doing an outside option in English Literature. Last week I submitted an assignment on Modernist Literature. On a Wikipedia article (I know, I know) I found a quote from a novel that was used to make a point (this point had been attributed to a published academic). I felt that this quote was perfect for making a point that I wanted to make. The point I wanted to make was similar but not identical to the point made in the Wikipedia article (in fact my point contradicted it but explored the same theme). So I used the same quote from the novel, cited the quotation form the novel but did not cite the article that had also used the quote.

It was in no way an attempt to deceive the examiners. I did at the time think briefly of citing the article but didn't know how to do it without giving the impression that the article was making the exactly the same point that I was making (and therefore twisting another author's words). Furthermore, the point made in the article was not a particularly novel one. It explored a common idea about Modernist Literautre. I know that as an undergraduate student, I am not yet expected to make academic discoveries that are completely unique, so using a commonly held idea is fine. However, some individual words that the Wikipedia article used were also used in my point (although the writing was ALL my own). That combined with the fact that I used the same quote from the novel, I fear will get me in trouble.

I really am an honest student. I am at a top university and have always loved studying. I am in my second year and have done well so far. In order to avoid the risk of being penalized for plagiarism, I did ask to resubmit my coursework and just take a mark reduction, but they said that this was not possible. I have been given no indication that they have detected anything yet, but it's eating me away while I really want to be revising for exams. Furthermore, I want to do a masters and if plagiarism goes on my record, the odds aren't good for that. Is it likely that I'll face this consequence?

It's better practice to cite from the original source if you can find it. You can provide commentary on secondary sources (quoted or summarised and referenced) to add depth to your use and analysis of the quotation but providing you referenced the quotation correctly you haven't plagiarised.

Try using google scholar rather than Wikipedia.

I think you will be alright, especially if you have cited the quotation from the novel. If your argument only slightly resembles the article then I wouldn't worry