Principled BSDF Glass Issue

1. Add a lip to the cup. This will help guide the direction of refraction rays. Most cups have a rim, and the glass shader is physically-based, so you're probably going to get weird results if you deviate from the real world.

2. Increase glossy bounces to something dramatically higher, like 64-128. This will help ensure enough glossy (reflection) bounces hit the rim of your cup. Also up transmission bounces to something like 64. This will help stop refraction rays from terminating too early.

3. Add an HDRI, more lights, and/or simply add a box or some other objects surrounding your cup. The environment is mostly causing this. At the moment, your world color is just a flat color, and you only have a small pink plane that the cup rests on. There's very litle for light to reflect off of, so you get too much refraction where there should be reflection.

See: Excessive refraction at glancing angles with glass and/or fresnel nodes?

This is how it looks when I upped glossy bounces to 128 and transmission bounces to 64. I think it's significantly improved already. It's not perfect though, and you can further improve the realism following my other steps. Most important is an HDRI or some other more realistic environment instead of endless empty space.