Cat scan was clear but an ultrasound showed a shadow on liver and stomach. Should I be worried? Blood work was fine.

A "shadow" on. ultrasound is not a specific finding and could mean almost anything. It may be normal, particularly if the CT showed no abnormality. What is the specific abnormality mentioned in the US report, if any?
No worries. The Cat scan is more precise than the ultrasound and this is why is used as a confirmatory test if the ultrasound shows something abnormal. So, if the Cat scan is normal, don't worry about it anymore. May I ask why did you have the ultrasound done in the first place?