You want to look this up in your adapter settings via de device manager and see if you can manually force it to 1000baseT (1Gbit) and Full Duplex, because your test clearly shows a 100Mbit upper limit. Second (this happened to me on a bad cable on ethernet on a MacBook, but might also happen on WiFi and Windows) is that the interace unfairly gets downgraded to 100baseTX.
First try to disable autotuning via the command line netsh int tcp set global autotuninglevel=disabled
