I understand your feelings completely as I have a much more severe case of pectus carinatum than you. I was bullied at school and became deeply depressed for years. I was always worried about how my chest looked with clothes on and off and what a girl might say if they touched my chest. Some thought it was hard muscle, which I would feel shame about anyway as it was a lie, whilst others would point, touch, stare and ask 'what's that?' - I would die inside - It really held me back in life and contributed a lot to my depression.
I contemplated corrective surgery - there are 2 surgeries you can have - Ravitch procedure and the Reverse Nuss procedure. I met with two surgeons. Both of these surgeries are highly invasive though and I decided against it. I don't believe you need to do this.
I know this will mean nothing to you, but your physique is great. You have a VERY mild PC. As someone above said, you're blessed with a wide shoulder frame and narrow waist. I had a similar frame to you at 21 and decided to hit the gym A LOT to add bulk to mainly hide my chest. I was a typical Ectomorph (hard gainer) and 198cm tall, so I had to eat a lot and work out a lot to see any gains. I added a lot of bulk to my chest and shoulders, but it took me years. Building muscle is a long, hard process. It takes dedication and desire. It can feel sometimes, particularly when you're young and an ectomorph, that you're going nowhere. KEEP GOING. I also would always walk around like a boxer with my shoulders rounded forward to try and sink down my chest. I became big and muscular - but I was still not happy. Why?
The reason I was never happy was because I hadn't accepted myself from within. You will always live with PC, this is who you are. It's ok to be different - as hard as that is to hear, and it took me YEARS to acknowledge this fundamental to happiness. I had never learnt to love myself. I was constantly trying to chase and build a chest that I thought others would find acceptable, but I realised in my 30s that I would never achieve this as I had a warped perception of what I thought i looked like. You will only find happiness from self acceptance. And you know what? As soon as you find this, you will be happier, calmer and more confident. Girls will find you sexier because you own your shit and are comfortable in who you are.
The people who comment on your chest are almost certainly doing it from a place of self loathing about some part of their own body or something else in their lives. Anyone who accepts themselves is unlikely to want to put anyone else down. It might not be clear and obvious to you, but I guarantee this.
Go hit the gym - eat a lot of healthy protein rich food, protein shakes, creatine - build a strong, muscled body - but know that this will unlikely make you happy. Really commit to self acceptance. I cannot give you better advice than this. You will save yourself years of pain and misery. Eventually, with age, this will come, I just wish I'd given it a chance when I was your age instead of hating on myself so much.
I don't mean to minimise your experience, I really empathise with you. The pain and depression and shame is real, I'm just giving you advice having lived with the condition 13 years longer and know exactly what you're going through.
I'm now 34 and through injuries haven't been able to train as much as I used to. I'm nowhere near as muscular as I was in my 20s but I'm so much happier and at ease with my chest as a result of accepting and trying to love who I am.
WORKOUT notes. To add bulk as an ectomorph, you want to be hitting the gym at least 4 times p/w and eating a lot of clean protein rich foods. Leg days are as important as chest days. The body needs growth hormone to really build muscle and this is created through muscle stress. Your legs are your biggest muscle group so create the most growth hormone. Growth hormone circulates through the whole body so working out your legs will also help build your chest, shoulders, back and arms. You want to be obviously bench pressing heavy and full range of motion. I always found dumb bell pullovers a good outer chest builder too.
Best of luck mate.