Another setting to look at - is Windows 10 Control Panel configured for 48k? - as per (example only):
Beyond that, I've run out of possibilities.
EDIT: If you have an audio editor such as Audacity, Sound Forge, etc. does the mic record in 48k there? If it doesn't, then the problem is not just with Vegas Pro but somewhere in your system. However, if it is only Vegas Pro which records in 44k rather than 48k, then a reset of Veas Pro may be needed:
While of course I do not know your recording process or requirements, do you definitely and absolutely need to record directly into Vegas Pro? In my case for VOs, I record into Sound Forge at 48k in sentence or paragraph chunks, edit in SF and then import the .wav files into VP. Again, this may not work for you.