Hey dj-22,
If you are having a print quality issue with the Officejet 4620, then I would advise taking a look at the steps in the document linked below.
Troubleshooting Print Quality Issues
If the steps do not address the issue, then keep in mind that the printer comes with a 1yr factory warranty. If you got this printer only 6 months ago, then the printer is still in the manufacturer's original warranty period.
Jason