When you apply to a graduate program, you are evaluated on a number of different factors by the committee. Grades, and home institution are part of that. But they are just pieces of the "you" that you are to present as a whole.
You will also be evaluated by your pGRE scores, research, SOP, letters of recommendation.
Since you're from a no-name school (assuming), and you didn't do as well in HS, what you can really focus on is gaining a strong upward trend in your grades. A B or C your freshman year begins to hurt a bit less when you continued the sequence with A's.
Develop a good working relationship with a few of your professors.
Get involved in research. If there is no research opportunities at your university, there are excellent opportunities via REU programs.
Really, the worst case is that you take the Masters somewhere, and then do the PhD. But I'm sure you if you work at it, you'll be capable of presenting a product that graduate schools want to buy. They want to know you'll be able to keep up with the pace of the work and produce papers.
Cheers