Top Law Schools

2L part-time student at a T30 school. Got offered a full-time law clerk job in a particular field of law at a mid-sized firm. Pay is generous - $54k + benefits, which combined with my scholarship would cover nearly all costs of law school. My only concern about it is that I'm not sure if I'm 100% interested in that field of law for the long-term, as it is generally a field that only has small to mid sized firms on the plaintiff's side.

I've heard that your first real legal job determines what kind of law you'll be doing. How much should I be concerned about being pigeon-holed into this field if I take the job (which I probably will be doing)?