Froze on YouTube screen while shutting down

I was watching YouTube videos before I went to shut my Mac down and I had quit all my apps, when I shut it down the screensaver was there and then all of a sudden a photo of what I was watching on YouTube came up and it showed the loading signal and shut down. I see the screensaver sometimes during shut down but this has never happened before. I'm not sure how else to explain, other than I was shutting it down and an Apple Logo and watermark from the YouTube video I was watching came up. (The Apple Logo was part of the video) It's hard to explain, I got it recently so I'm pretty sure I still have warranty. Should I be worried? Because I sure am! I saved my money for a YEAR just to buy this computer!