I got 600cc Silicone implants under the muscle on November 27th. They are not big at all? (photo)

With so much implant up near your collarbone, they will seem small because of how they probably don't fill the cups of the bra you wanted to fill.  They also seem small when they are filling near your armpit more that at the bottom fold level.  Be patient and do your exercises to get that lower pocket able to accommodate what is really a large implant for your frame.  They will seem much bigger then.

Breast size is a very personal issue and you made the best judgement you could based on all information you could gather beforehand. It would be important to give the implants a minimum of 3 to 6 months to allow them to settle and drop. They will not get bigger as they settle and may even feel just a little bit smaller. You can always exchange to bigger implants later but let these settle and you adjust to them before making a decision for an implant exchange.

It's difficult to assess proper size when photos are viewed on plastic surgery websites.  Breasts always look bigger in the photos than in real life because of a "photo-illusion" effect.  This means that because the photographer is close to the subject, there is an illusion that things are larger than they appear.  Also, if you looked at photos of 600cc SALINE implants, then they definitely would look bigger than 600cc silicone implants.  Silicone implants conform better to the ribs so they don't project as much as saline for the same volume.  In addition, yours are still high.  When they drop, you will project more. Be patient for another couple of months and I think you will notice a better shape and more projection.  Hope it goes well!