Cheryl - I have the exact same jacket (Century in women's medium) and it's a bit large on me as well. In general, I don't like loose fiting clothing on the bike, but in this case I find that I don't mind the larger fit. It actually gives the air a little room to move on the inside. If it's pouring, I'm not going to be riding all that fast anyway, so extra flapping material is not a concern. What I have found is that this is now my go-to jacket for really cold temps. I can regulate heat well with all the zip options...and with the extra room, I can put extra layers underneath just fine.

I don't think I could go smaller anyway as the body would be too short on me(I'm long waisted). I do like the narrower waist and having plenty of hip room though. Now I just need to get off my duff and order the hood!