With the temperature in the room at 30-33c and with your PC in a location that blocks air flow you can't expect much better CPU temperatures than you are getting.
I would move the PC so it gets better air flow, remove the side panel and point a fan at the motherboard.
My case is the Corsair Obsidian 750D Airflow Edition. It has 3 fans pre-installed, so I don't think the airflow is the problem. The problem is where I have the case. I agree that in that space airflow is limited, but I'll not use the stock cooler for long, because I originally had a corsair h100i v2 and I'm waiting for the am4 bracket kit to arrive. Once I install the AIO, the temps will be fine. But I'll try to move my case somewhere else, because I don't like where it is right now. But the temps I'm getting with the stock cooler I think are perfectly fine, especially when gaming. I don't really care about idle temps, so I'll be ok until the bracket arrives.
Edit: I forgot to mention something. While installing the stock cooler I didn't apply any thermal paste to the cpu's surface, as the cooler had some pre-applied. Should I open it and apply some thermal paste or is it ok?