Supporting multiple VLANs on a switch interface means you will have a trunk with tags to separate frames for each VLAN on the trunk, except the native VLAN (if any). On your Cisco 350 switch, you can restrict which VLANs are allowed on a trunk:
switchport trunk allowed vlan {all | none | add vlan-list | remove vlan-list | except vlan-list}
For example, assume the user VLAN is 45, the guest VLAN is 46, and the trunk interface to the WAP is port 48:
interface GigabitEthernet48
switchport mode trunk
switchport trunk allowed vlan 45,46
!
Most end-devices do not understand VLAN tags, and they will drop tagged frames as giants. If you are concerned about someone making unauthorized connections to your switch interfaces, then you need to use 802.1X, but that will require some work to set up the infrastructure. That switch model supports 802.1X