I'm flying in from Guilin to Beijing Capital Airport, arriving at 21:00.

According to your situation, it is an domestic to international transfer from T2 to T3 at PEK. And you have 2 hours and 45 minutes to catch the next flight. Generally speaking, the minimum transfer time is 160 mins. Thus your time is tight. You need to finish the procedures ASAP. Or if possible, you are advised to change the schedule of your next plane.