I typed in my IP into my address bar and my router admin page came up. Is this safe? How can I disable it? It's Linksys Smart Wifi
You may already be safe: if you typed your IP address into the address bar of a computer connected to the router, being able to access the router admin page is normal. The router knows your computer is on the "inside" part of the network, and should be allowed to control the router.
The only time you have a problem is if you type your IP address into a computer somewhere else on the Internet (such as at your local library) and your router admin page shows up: in that case, you need to disable remote administration through the admin page.
You're most probably in a private network IP range. It is not accessible through public network (Internet)