Technically you do, but I wouldn't worry. I doubt your videos are seen by that many people, and if anyone did come across your video and took issue with your breach of copyright, the most that would happen is they would politely ask you to remove it from your site. Don't worry about your PC being confiscated etc. - that never happens for such a minor offence. There are literally millions of small homemade movie clips on the net that use music without copyright clearance. This doesn't make it right, but it's not an area in which you need to worry about serious legal repercussions.