should grind to get coffee running from group slowly 20s to 30s
also use same amount of coffee and tamp each time.
make sure machine is warmed up well at least 5 to 10 minutes, portafilla should be hot, try brew espresso when ready light comes on, (this means its hottest temp as thermostat turns off ) , see how it taste. then try brew when ready light turns off (temp at coolest, thermostat just turn on)
gaggia do have a wide temp swing , you can temp surf by timing from when read light goes off or on.
you can do search on youtube to see people brewing espresso to get idea of time and volume poured.