Lana -- a few thoughts:
First, if you're curious about what attorneys who practice criminal law do, see if you can get ten minutes to chat with people who practice in local DA's offices and criminal defense firms. Many people would be happy to talk with you for a few minutes about what they do. Your school's career center should be able to provide you with tips on "informational interviewing," and you should definitely do it. You might also be able to secure an internship or something with a proscutor's/DA's/defense attorney's office that would give you an opportunity to see for yourself what goes on there and would help you decide whether to pursue that.
Second, I want to say a thing or two about your concerns about your grades. Valkyrie is right that you don't necessarily need to go to a first-tier school to get into criminal law. If, after some informational interviews, you find that the practice of criminal law as an attorney is what you want to do, but you have trouble getting into the schools that you want to attend, you can consider taking some time to do other work, perhaps work that would give you more insight into the legal career that you're thinking about. For example:
- Quite a few people who entered my law school class had already spent a few years as paralegals. Becoming a paralegal requires a bit of specialized training, but the certification programs usually don't run that long.
- You might be able to get a job working as an administrative clerk for a judge whose caseload is primarily criminal. Those jobs are not known for high pay, but depending on how the court works you might be able to get some time observing in the courtroom. People who go into law after working court jobs say that one of the most valuable opportunities the court job provided was the opportunity to see good lawyering and bad lawyering and understand the differences (and sometimes hearing the judge's private point of view back in chambers after hearings). If you see jobs like that opening up, ask people at the courts what the jobs involve. (Note -- the kind of job I'm talking about is different from a judicial legal clerkship, which goes to new law graduates and involves more legal research.)
- I know absolutely nothing about what kind of training is involved, but you might seek out some specialized training in criminal investigation. Both prosecution and defense require investigators, though the government tends to have access to more resources. If you're at a large school, there may be classes in, say, forensic investigation directly available to you. Even if you can't get those kinds of classes, if this path sounds interesting to you, you might consider taking background classes in chemistry, biology, and/or psychology. Your major field probably requires plenty of courses in the soc/psych area already. If this is a route you're curious about, there are people in police departments, state bureaus of investigation, and crime laboratories who could tell you what training it would take, beyond your Bachelor's degree, to do it.
- Even if you were to do something completely unrelated to criminal law after college, it helps to remember that as college recedes into the past, so does the significance of your college grades. Life experience can count for a lot.
All of this, of course, is "do as I say, not as I do." I went to law school right out of college, having gotten into a school I wanted to attend. I also went to law school having very few clues about what I would do with the JD once I got out. But my point is, if you decide that criminal law is what you want to do but you don't get into law schools that (after research) you think will give you what you need, there are lots of options that would give you connections to the field. The background experience they offer would not only increase your law school opportunities, but would also help your employment opportunities beyond law school regardless of what school you attended.
I also have to include the caveat that I'm not a criminal lawyer, and I haven't had much training in criminal law. Valkyrie might tell you that I'm off my head (you practice crim law, right, Valkyrie? or have I confused you with someone else in that regard?).

I'm just brainstorming a bit here.
Okay, that's more than a few thoughts. I hope something in there helps or gives you some ideas as to what you might do!