Shy to the point where I may seem rude?

Just today I went with my family to a relatives' house for a visit, but I didn't know what to say to them so I just went off somewhere to hide from them as usual...My dad scolded me today for NEVER greeting them and I felt extremely bad and extremely rude. I felt bad because I like them and I didn't mean to be so shy but I really didn't know what to say to them and I was afraid it would be awkward cause that's how it usually ends up... I mean I just walk in and go off to the corner... I want to make it up to them next time I visit, but what should I say?? It's going to be really embarrassing since I never said anything to them before...I'm really antisocial.