API keys and secret are a pair that opens access to your account. Also, API secret is shown only when it's created. As long as you didn't record it or share it with anyone, there shouldn't be any problem. Also, make sure to check off boxes that do not apply while creating an API key. If you are using services like BearTax or any portfolio app, give only read access and remove trade/withdrawal access. That will ensure the security with API key even if attached with some application.