You can safely take a lot. Each EmergenC packet is 1,000mg, and if I'm sick I take 3 packets a couple times a day. The concern about contractions is probably because if you take more than your body can handle at once, it gives you some loose BMs, which might set off some cx's. Maybe start taking 2 packets at a time, like 2-3 times a day, and see how your body handles it.
At this point in pregnancy it's fine to take normal amounts. Very large amounts in early pregnancy can cause miscarriage, but I think you have to take quite a lot even then, and it doesn't have that affect later in pregnancy. I take 500mg a day in addition to my prenatal for an immune system boost.