First, stop trying to feed it Goldfish, they are of little nutritional value and can introduce disease and parasites. I realize you said it’s not eating but have you noticed any white stringy poop? Are you keeping up with tank maintenance? Weekly water changes, filter maint, checking parameters?
A good quality pellet is much better for your fish, NLS, Hakari Bio-Gold+, Hikari Massivore ECT along with frozen or freeze dried Krill, market shrimp and night crawlers as treats used supplementary with the pellets is a good diet.
How long have you had the fish? I agree it may take a while for it to settle into its new surroundings, that being said the stomach distention is concerning as that doesn’t occur in a week, so how long has it been since it’s eaten? Was it eating when you first got it? One other question is what temp is the tank? If your keeping it at the mid to upper 70’s I would bump the temp up to around 82 warm water increases the fishes metabolism and aggression and barring any other problem usually gets them eating. Good luck.