Hi Leanna,
Yes, you can have both Point-to-Site and Site-to-Site using same VPN Gateway resources.
From the VPN Gateway FAQ:
Can I have Site-to-Site and point-to-site configurations coexist for the same virtual network? Yes. For the Resource Manager deployment model, you must have a RouteBased VPN type for your gateway. For the classic deployment model, you need a dynamic gateway. We don't support point-to-site for static routing VPN gateways or PolicyBased VPN gateways.
Please see tutorial article below for setting up Site-to-Site. Since you already have existing VPN Gateway, you can review Prerequisites and then skip down to Create a local network gateway step and continue from there.
Tutorial: Create a site-to-site VPN connection in the Azure portal
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Thanks.
-TP