When you design a website, it's difficult to estimate how good the performance and security really is.
You can visit your website over a slow connection to get a general feeling for its speed, but this is just one other data point and doesn't really tell you the reasons. The lock in the browser address field shows how the connection to your website is encrypted with SSL, but not much more about the security.
A great tool for such cases are website speed and security tests. These tests don't just measure the loading time of your website or used SSL certificates, but also analyse the structure and content of your website to give you hints how to improve it.
You don't need a perfect score in every test for your website to be perfect. There are always things only your hosting provider has control over or necessary tradeoffs specific to your website, which will prevent you from getting the best score. Still, you should aim to get a high a score as possible and repeat the tests at least once every year, because the technologies behind your website and possible attack scenarios are constantly evolving.
Here are some great free tests I recommend to you:
Qualys SSL Labs
HSTS Preload List