If the reason you are feeling pressure on the fingers is due to your lips being pushed inwards and forwards from engagement in the aperture corners, then you are doing great.
It is also possible, unfortunately, to engage the lip muscles themselves directly and to form a pucker with tightly engaged lip muscles–lips that are tightly engaged do not vibrate as quickly as relaxed lips, so that will become a problem at a certain point as you ascend and the tone will not be as resonant as if the lips were more relaxed.
Unfortunately, only you can determine which is causing the pressure.
Generally speaking, Less Is More–the less we engage, the more resonant the tone and the faster potential vibration the lips can achieve.
My understanding / experience has been that we want the tension at the sides of the mouthpiece, outside of the air column–where the lips interact with the air like the vocal chords, etc.