Trying to understand my first paycheck

Hi guys, I’m a new ITS1 and just got my pay in the mail.

Surprised how much I got for about a months work. I started my position around Aug 6, and was promised to be paid 6.3k a month on the final offer letter. Instead my earning reflected 5.46k a month, 1.6k deductions, so my net was 3.8k.

Most of my deductions were from 1.4k in retirement (not sure what plan I did??)

Is something off or does this all sound right so far? I’m new to state jobs so I don’t know all the details. Is there a calculator to accurately determine my next paycheck?

Thanks!