Serial.println statements do not work
They do for everybody else.
only 3 wave files can be included in the code
Highly unlikely, you have another problem.
I am not a programmer
And you never will be if you don't learn to debug code in a methodical manner.
I am a graduating electronics student
Debugging in a methodical manner is equally important for an electronics engineer.
posting more soon
Will you try what people suggest then?
Anyway I guess you have what you need for today, good luck with the course.
Rob