Lg 24UD58-B not high resolution?

i have bought a 24UD58-B lg display for my new Mac Mini and have set the display to default in system preferences, . It's connected via HDMI. It doesn't look very high resolution to me (i do work with a lot of fine text). when i hover over the 'larger text' scaling box, which appears to be exact the same setting as the default setting it says 'looks like 1920 x 1080'. Is there a way i can find out what resolution the screen is actually showing? I've looked at 'about this mac' and it says 3840 x 2160. It looks a lot more pixelated than my 2013 mac book retina 15 inch screen. I've spent an hour with LG and an Hour with mac support and neither could help me. does anyone else use this screen, if so could you let me know what the system prefs say? thanks!