A few thoughts:
- Can you return it?
- Is it the same cord as on your preamp? Have you swapped cords on the pre-amp and amp as an experiment
- I don't view it as you threw money away if you are enjoying music and the process. If you can't return it, perhaps you can sell it or even let a friend experiment to gauge their experience. (I'm making the assumption, you are disappointed but still have a lot of things to be grateful for!)