Question about espresso - eviltoast

Hi, I have recently got a Gaggia Classic Pro. So I am quite new to espresso. After I pull my espresso shot, the grounded coffee puck has imprints of shower screen (photo attached)

Is this normal? If not, how do I solve this?

I am filling it up with 18 grams of pre ground coffee (commercial espresso fine grind) in a pressurized basked.