I'm a 360cc should I go for a 450cc?

Yes, it is likely that you will see a difference with about 90 cc increase in breast implant volume.   The much more important question with be: will the 450 cc breast implants be the correct choice when it comes to  achieving your desired outcome when it comes to breast size…?   Whether or not to proceed with revisionary breast surgery: generally speaking, I advise patients to carefully consider their degree of concern with the outcome of the initial breast surgery and weigh these concerns against the potential risks/complications associated with the planned revisionary breast surgery.   For example, if the patient is concerned about her breast appearance on a daily or frequent basis, it is likely that revisionary surgery will be helpful when it comes to improving her quality of life.  On the other hand, if the patient's degree of concern seems minor and/or she is  infrequently concerned about the areas of concern, I would recommend against revisionary  breast surgery.
Generally speaking, the best online advice I can give to ladies who are considering revisionary breast augmentation surgery (regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals  with your plastic surgeon. This communication will be critical in determining  breast implant size/type/profile will most likely help achieve your goals. 
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as  “natural” or "C or D cup” or "much difference" etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on   who makes the bra; therefore, discussing desired cup  size may also be inaccurate.   
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery ( after the use of temporary intraoperative sizers).  Viewing the patient's chest wall in the upright and supine positions, with temporary sizes in place, help select  the best breast implant size/profile for the specific patient.
 Best wishes. 

Dear 143kyla,breast implant type and sizing selection is a complicated process and requires a detailed consultation that includes a discussion of your goals, a detailed examination, and a lengthy discussion. But the decision will always start and end with the patient. When it comes to sizing, we have all of our patients find 3 photos of their desired breast size. We ask for naked breast photos because clothing can obscure the true size (push up bras). Next, we consult with patients and go over the photos and take detailed breast measurements during a physical exam. Next, we using a sizing algorithm to determine a range of implants that will work based on the exam and the measurements.Lastly, during the operation, we use silicone sizers in the operating room to see how the size actually looks in the breast. We sit the patient up in the operating room, while asleep of course, and compare the sizer result with their desired look photos. If it is too small, we start the process over with a slightly larger implant. We don't stop until we get the perfect match.Of all of my breast augmentation patients, every one of them has been happy with their size due to this detailed and meticulous process. You don't want to invest time and money into a result that is either too big or too small.You should discuss your concerns with a board-certified plastic surgeon and make sure that your surgeon understands your goals.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Are you already looking top heavy?  If not and implants with the right dimensions can be obtained, you probably can go larger but you will have to find yourself another surgery since yours is limiting you.  But if you're petite and top heavy already, I can understand your surgeon's concerns and reservations.  So its going up 90 cc's worth it?  It just depends on whether it will make you happier as there are risks, costs, and healing that you will have to be accepting of and only you can make that decision.