Relax. First of all because you did average the first semester, you probably will not even be on academic probation, even if your last grade is a D. At worst, if your last grade is an F, then you may have to retake that class. Second, think about what you did different from last semester that may have led to your lower grades. Also, see if you can meet with your professors to review where you went wrong on the exam. Third, remember the saying, "the A students become professors, the B students become judges and the C students practice law and make all the money".
The only thing your grades will preclude you from is participating in on campus interviews. Considering only the top 10 to 20 percent do on campus interviews, you like most of your class mates, will have to find a summer associate position on your own. Luckily you are in a great position to find an associate position, because you are already working for a firm. Start networking at work, talk to some of the attorneys, see if you can find a mentor, or see if you can join the incoming pool of summer associates. Plus, your grade situation is more understandable if you are working while going to school.