Is my silicone nose implant too big? (photo)

There is a significant amount of swelling that develops after surgery of the nose, and it can take 6-12 months for this swelling to resolve.  The swelling that you have present 18 days after your surgery will affect the appearance of your nose and make it look larger than it really is.  With more time, the appearance of your nose will change.  I would wait at least 6 months and then re-evaluate your appearance.  It sometimes can take even more than 12 months to see the full results after the surgery.  

Hi and welcome to our forum!
The performance of rhinoplasty involves the separation of the nasal
bones and cartilages from overlying and underlying structures, fracturing
the nasal bones, removing excess bone / cartilage, reshaping of the
remaining bone and cartilage, and in your situation, placement of an implant. The significant intraoperative trauma
causes swelling (which may be asymmetric), which will make your nose look
large and wide. This will improve markedly over the first 6 weeks, but will
take at least a year for your nose to assume its final shape and size. It is far too early to assess your final appearance as the result is still camouflaged by swelling.
Continue followup with your plastic surgeon. 
Best wishes...