As long as you get your applications in by each schools' deadline, you should be fine. I took the Dec LSAT too and just mailed my stuff off yesterday. You may be at a slight disadvantage at some of the more competitive schools you apply to.
LSDAS gpa may be different if you took, for instance, summer school at another school and got a C. Your UG school would simply give you credit, ignoring the grade. LSDAS will count the grade regardless. So if you have a 3.5 from your school, but 9 hours worth of C's from another summer program, your LSDAS gpa (the one schools will be looking at) would be a little lower.