What am I doing wrong??
to answer that you'll have give us some actual information on what you are doing.

You've got underextrusion. It could be down to printing temp and or speed. People tend to print much faster than they should. Manufacturers habitually put ridiculously high print speeds down, that just aren't practical.

It could be down to a partially clogged nozzle.

For pet-g I use 245-255 print temp, no faster than 50mm/s print speed and a bed temp of 75c

So what print settings are you using ? Slicer ? etc