I always used to get the 'Doesn't contribute in class' at parents evenings, both at high school and college.
I was kinda like you with my G.C.S.Es, getting good grades with not too much work. And yeah, college can be a bit of shock as most people who were getting As at GCSE will now be getting Bs and Cs. But don't forget that the grades work differently so Cs are average. I was really pleased to manage a B in English Lit.
I wouldn't worry about your grades too much at the moment. Grades can change from one term to another. i don't think i ended up with any of my predicted grades. just make sure you do the work.
And I'm sure that you've nothing to worry about at the parents evening. I used to hate them but was always ok.

I got predicted D/E for Science and came away with a B, so I would ignore predicted grades...