My boobs don't look or feel any bigger. Why is that? Will it change?

I am sorry to hear about your concerns after breast augmentation surgery.  Yes, although I cannot predict whether or not you will be pleased with the long-term outcome of the procedure performed,  I can tell you that I do expect that the breasts will change given that you are only 3 weeks out of your breast augmentation procedure.  Of course, your plastic surgeon, knowing the details  of your situation, will be your best resource when it comes to good assessment, advice, and/or meaningful prediction/reassurance.
Generally speaking, breast implants will "drop" into the pocket that was created during surgery. The rate of breast implant "settling" may depend on factors such as size of breast implant pocket dissected, tightness of the overlying skin/muscle layers, and size of breast implant utilized. Normally, it takes about 3-6 months (for some patients longer) to see the final result. It is very common for one side to settle faster than the other.
Similarly, it takes a few months for the breasts to "soften" in most cases.  Most of my patients tell me that their breast implants feel "part of them" somewhere between 3 to 6 months after surgery was performed.
Many of my patients report that as the swelling around the breast implants (for example, in the sternal area) decreases, they feel that their breasts appear more projecting. Also, in my opinion, the "drop and fluff” phenomenon does hold some validity; as breast implants “settle”, many patients feel that their breasts actually look larger. 
 There is definitely a physiologic and "psychological" (body image)  adaptation process that occurs, at differing rates for every patient, for patients who undergo any type of aesthetic surgery, including breast  augmentation surgery.  Understandably, patients often experience significant emotional "ups and downs" around the time of surgery.
 
Best wishes for an outcome that you will be very pleased with.

The most important thing for you to remember is that you are very close to your surgical date. Many changes will take place. If your implants are under the muscle, the muscle will relax over time and allows the implants to take on a new shape. I consider that at about three months, you should be able to better analyze the situation and understand your final results. If you have concerns at that point, you should certainly discuss them with your plastic surgeon.

265cc implant is not a large implant.Depending on your chest dimension, 265cc can increase your cup size 1-2.You are still early in your recovery process.  Your breast shape will continue to change next 3-6 months.  As the implants settle in their pockets, breasts may appear slightly fuller.  After 3-6 months, if you still feel that your breast size is not what you had expected, you may need implant exchange.Good luck with your recovery.