If he doesn't have any tankmates, he may be a bit timid. Mine seem to be more social when they're in the company of other fish, particularly other larger cichlids. I always quarantine my pikes in bare-bottom 20 gallons and they tend to hide and act shy. Once I move them out of quarantine and into my cichlid communities, they're much more friendly and rarely hide.
Do you have another larger tank you plan to move him to? At 3" he'd probably be okay with other peaceful cichlid tankmates like Geos or severums. If you have a suitable community, try moving him and see if he gets a bit more brave. Keep in mind that it may take him a week or two to adjust to a new tank, so you'll probably see more hiding until he feels comfortable.