Bike pump gauge showing low pressure
I'm pretty new to cycling (haven't done so for about 15 years), and I've recently got a bike to speed up travelling to uni. I have a bike pump with a gauge, but I'm slightly worried about trusting the gauge on it.
My tyres are rated for 50-85 psi, and I'm currently hitting around 40 and they feel pretty solid to me, and I'm feeling some resistance on the pump at the moment and I can hear the spokes twanging every now and again, so I'm rather concerned that trying to pump it up between the specified range might be too much for it.
Should I go any further with it? Could the gauge on the pump be wrong?
This all is probably because I'm inexperienced, but any advice on the matter would be helpful!
For reference, this is my bike:
And this is the pump I'm using:
Thanks in advance.