I can only achieve 100Mbps not 1000Mbp on LAN?

According to my motherboard here https://www.asus.com/nz/Motherboards/PRIME-B250M-A/specifications/

My network adapter supports 1000mbps but the adapter settings are stating 100Mbps.

I've updated to the latest driver and I tried using a cat 6 and a cat5e cable

When I did a speedtest on my mobile and laptop it was capable of going above 100Mbps

So would anyone whats preventing my PC from going above 100?

My flatmate tested his laptop using lan and achieved 800