I wouldn't think that you've messed anything up. I was on enbrel for many years, and I always took it if I just had the common cold. If it was a full-blown sinus infection, however, I would hold off until I finished the antibiotics. I think it's probably ok with just a cold, but you could always ask your doctor his/her preference.
I started orencia infusions; I've had two and going in for the 3rd one this week. I've had a great response so far, but it only lasts a week or so before I'm back to square 1. I've been told it can take orencia 5-6 months to build up enough in your system to truly have significant effects. I'm optimistic, though, since I do have a few days relief directly after an infusion.
Hope you feel better soon.
El