Bit late in the day but for the future I highly recommend either learning to use some music editing software (or better still software to actually make your own songs) or finding somebody who is a bit handy at that kind of thing.
At the very least download Audacity which is easy to use and will allow you to do basic editing and some tweaking of songs (song length, splicing, speed, tempo, fading in/out etc)
It can be handy not limiting your choice of music to a track that is exactly the length of performance you are planning.
I've tweaked tracks for myself before and worked with a friend to lengthen a short edit of a tune, putting in some little cues to help me work out where exactly I was, very helpful.
