I had a full scholarship to the University of Louisville. My parents wanted me to go pre-med, so I did, I had no idea what I really wanted to do and felt like school was a waste though, I was always very physical(football, rugby) and I was smart, I wanted to do something that involved both. Dropped out and started working various jobs, ended up in HVAC at 19 and I've been hooked since.
If you are tough, love the feeling of a days hard work when you get home, naturally inclined to succeed at this occupation and want to learn to get better everyday... You will succeed in this field.
I would a recommend a summer working as a minimum wage helper and getting your but kicked on installs to see what you think of it. You might just need something like that to get you a little more "motivated" to succeed at school and find something you want a degree and career in.