I have cut down my music using itunes, when I drag the music onto a USB file the music goes back to its original length. How can I stop this?

I have a party coming up where I have to provide all of my own music, the majority of my music takes a few seconds to start or has seconds added onto the end after the song has finished playing which doesnt sound good on a party playlist. I cut down all of my music which I was very happy with but when I drag the music onto my USB file all the music goes back to their original lengths. Is there any way I can stop this? Or can anyone reccomend me another trimming software which is easy to use and FREE. Thanks 🙂