First of all, you’re walking into college with a 3.5. Congratulations—that’s a most excellent GPA.
As for your main question, there are two different but equally important answers.
First, whether your college counts those grades as part of your GPA for things like Latin honors at graduation depends on its own policies (which will be mentioned in the catalog). I’ve mentioned elsewhere on CC that I flunked out of college my freshman year; however, the college I ultimately transferred into didn’t count transfer courses as part of its GPA calculations, and so I received my bachelor’s degree magna cum laude. The university I work at now, on the other hand, does count transfer course grades, and so if I’d gotten my degree from here I wouldn’t have had even a remote chance at Latin honors.
Second, though, if you’re applying to graduate or professional school, all of your college courses will be counted in GPA calculations for entry—so your B in astronomy will count. However, the trajectory of your grades also counts—so, to take my case, even though I ended up with something like a 3.1 due to my horrible freshman year, the fact that my grades from year to year were 1.8-3.3-3.8-4.0 (including a 4.0 in my major) meant that nearly everywhere I applied to for grad school was willing to overlook that first year and admit me with funding.
That said, I return to the first thing I said—a B in a college course is a good grade. If you end up with a 3.5 overall for your college GPA, you’ve done better than the vast majority of students. (This is actually something that’s hard for a lot of students who were high-achieving at- or near-4.0 in high school to come to terms with once they get to the postsecondary level, but it’s true.) Yes, it means you will never have a 4.0 for your overall college career—but then again, nearly nobody does that, anyway, and to be honest that shouldn’t be your goal.
(Not to mention that it’s only 3 credits out of a likely 120 or more—that one grade is only 2.5% at most of your total GPA. Even if you’d gotten an F, it would only have lowered your potential GPA from a 4.0 to at lowest a 3.9. Getting a B? Even less of a hit. Seriously, don’t stress about it.)
