You're fine. A TLS certificate validates the server machine (or host machine), not the page or folder.
For example, all of
*.stackexchange.com shares a single certificate. By inspecting the cert for this page in Chrome:
Issued to: ssl333133.cloudflaressl.com
Subject Alternative Names: DNS Name=ssl333133.cloudflaressl.com
If you wanted to add more host machines each with a different domain name, for example:
then you might have to look at either getting more certificates, or getting a wildcard cert (
*.website.company.com). For your question: yes, you can add as much content as you want to the same host machine without needing to change your certificate.