I am so sorry you are unhappy with your results; I would bet your surgeon is equally dismayed, since of course he used all his experience and best judgement to try to achieve your goals!
Let's examine your situation in detail (at least as much as your included information allows): you are slim and petite, and after two children had smaller than A-cup breasts and loose skin. A lift alone would have yielded scars and an ounce less volume (skin removal) than your present quite small breast size. Unhappy result, and more costly operation (and you can't "take the scars back.")
You asked for "small, conservative" results, but did you try on implants to let your surgeon know just what that meant to YOU? (because it obviously meant something else to your surgeon.) Did you bring photo examples of just what "small and conservative" is to your mind's eye? Did you look at your surgeon's and many other website photos of patients with similar size breasts to yours, and what size implants gave them results you liked? If you didn't then perhaps this is a shortcoming of your surgeon's sizing process, because I suspect he can't read minds, and obviously missed the mark with your surgery.
Lest you be too hard on your surgeon, you should understand that 450cc is (by my personal estimation method determined over 25 years and thousands of breast patients) anticipated to add just under two cup sizes to whatever breast volume you started with. At AA before surgery, this would yield a full C cup (perhaps a D-cup bra from Victoria's Secret) for most patients. And of course, we haven't discussed the "(loose skin)" that did require a certain volume to adequately fill so that you wouldn't have a truly unhappy "rock-in-the-sock" result. 450 sounds like a large number, but it is a very common size for someone with loose skin and little breast tissue of her own.
Going down 100cc (just over 3 ounces, or 1/4 of a can of pop) will be a barely-noticeable decrease in size and will increase sag (same skin, less volume) somewhat. Going down 150cc will drop you by just over 1/2 cup size and will increase the skin laxity a bit more.
For now, I'd advise patience and continued follow-up with your surgeon without anger or "blaming." He truly wants you to be happy, and acknowledging that to him while calmly expressing your feelings (which you should understand may change as time goes by) is the prudent way to keep your surgeon on your side rather than defensive. You should also discuss (if you didn't already--always something that SHOULD be done PRIOR to surgery, IMHO) what revisionary surgery costs are and who is responsible for what. Being vociferously unhappy does NOT get you a "free" re-do; it often gets you another surgeon who charges full price. Be well and take care. Best wishes! Dr. Tholen