Chances are you’re having problems getting the pressure low enough.
if you’re doing it right, you’re pulling a vacuum.
the deeper the vacuum, the lower the pressure. you will occasionally hear a deep vacuum (low absolute pressure) referred to as high vacuum. what we call deep vacuum (0.75 to 20 microns), the physicists do not. they like to play in the 10-9 to 10-12 micron range.
first question: with nothing but your gauge connected to you pump, how deep a vacuum can you achieve? this is your blank off value.
now how about with your empty rotovap?
if you can’t trivially find your leak, you might try using helium.
use the search function to see what others have posted as appropriate vacuum levels for solvent recovery in a rotovap. eg Search results for 'rotovap' - Future4200