Should I open the CRT monitor?
Three months is not long enough.  I used to service several brands of CRT monitor.  I did the discharge procedure even on CRTs known to have been stored for months.  Indeed, quite a few still had a charge.

Just do the discharge procedure.  It's not that hard... and it's fun.

Safety first.  You are dealing with several thousand volts with enough current to potentially kill (or knock you out, which can cause secondary injuries). Make sure it has no possible path through your body. You should have nothing tying you to ground (no grounding strap), don't lean on anything or touch anything, one hand in your pocket.  Don't be tempted to grab the CRT to steady it, that's how you get shocked.