Yeah, you took on too much too soon. Should have ridden some short rides first to get used to the bike, not taken a longer ride when you already hurt. . But no problem - you'll be back in the saddle soon enough.
If the pain is all around the sit bones, that's good - they should be the part that carries your weight. If the pain is farther forward and central, you may need to adjust your seat. It shouldn't be digging in to your soft tissues.