Geologists/scientists, did you have any terrible grades in a science class? This post discusses lousy grades from an academic's (ecology) perspective.
In college, I caught fire in chemistry, stunk up my math classes, did ok in my geology classes, and was generally a better student in my non-major classes. That post I referred to also discussed my lousy high school science classes, which
temporarily convinced me that I couldn't hack "real science", so I won't rehash high school here. In the end, I got school honors as an undergrad, but not department honors. I didn't have that singular lousy grade, though.
When I was a senior in college and trying to figure out what to do next, I thought that only brilliant people who got all As were "allowed" into graduate school. None of my professors seemed to think I was good enough. Nobody said, "hey, have you considered grad school?" It didn't occur to me until much later that the only students from my department who went to grad school right from college were clearly preferred by the professors, who were aggressively "outdoorsy", dominated the class discussions, and generally sucked all the oxygen out of the room from those of us who were more reserved or unsure of ourselves.
Here's the thing. One bad grade won't keep you from being a stellar academic. One bad undergrad experience won't keep you from getting where you want to go, whether that's a "hard" science or academia, or somewhere else. I used to work with a science expert who had flunked out of college entirely. It may take some hard work initially. Maybe you need to build an industry reputation. Maybe you take a couple years to take (or re-take) some classes. But there are no iron gates preventing you from getting the experience/grades/confidence to get to the next step, whether it's academia or industry.