Why do I behave so awkwardly in social situations? Was this awkward?

'Oh good, you've got something in your hand now!'.

Are you a guy or girl? And I don't think you acted awkwardly at all.

Also it sounds like the first girl was hitting on you. You could have said something like: "Your hands seem empty too, perhaps you should hold my penis."

Were these people obese by any chance?

I tend to be quite shy in big social situations and always tell myself that I'm going to open up and talk more, but IT NEVER WORKS! I used to think of what I was going to say but have stopped doing that now, I tend to go with the flow. However, after every social situation, I just feel like an idiot and hate myself. Here's what happened today; I felt extremely awkward.
So I went over to a friend's place for a screening of a short handmade film he's made. There were a lot of his friends there, around 15 of them who I didn't know but did know one guy really well who I was with most of the time.(Anything wrong with that?). So after the film, there was some food and drink and after I finished eating, this girl comes up to me and says 'Why are your hands empty? There's so much food going around. Have something!'. I mumbled that I was full, but my idiotic mate made it worse and said, 'Oh come on, don't be shy, have something'.
Then later on, I was eating something and the same girl says 'Oh good, you've got something in your hand now!'. And I just smile awkwardly, SHOULD I HAVE SAID SOMETHING? And then the third incident, sorry for rambling on, but this guy came in with something on a tray and offered it to everyone. I refused, but this girl(not the same one as earlier) said to me, 'Hey didn't you want one of these'? I , again mumbled, 'No no, I'm fine' and again my mate went on 'Have some, don't be shy'. GRRR.. **** ..I just feel so odd and out of place sometimes.
Would anyone here have reacted differently? And now I'm thinking all sorts of situations, whether I should have said anything different or behaved differently or whether my friends would have reacted the same way in similar situations..

Hmm..thanks guys..should I take it up with my mate now? Tell him to please NOT keep saying that I'm shy as it annoys the **** out of me.

At least one person does.

This girl sounds annoying, I would have nutted her.

I'm more annoyed and frankly pissed off with my mate. I just texted him 'THE NEXT TIME YOU TELL NOT TO BE SHY IN A PUBLIC PLACE OR A SOCIAL GATHERING, YOU WON'T HAVE THE TEETH TO SAY IT ANOTHER TIME. WATCH OUT AND DON'T ****ING DO IT COS IT ****ING ANNOYS ME'.

I'm more annoyed and frankly pissed off with my mate. I just texted him 'THE NEXT TIME YOU TELL NOT TO BE SHY IN A PUBLIC PLACE OR A SOCIAL GATHERING, YOU WON'T HAVE THE TEETH TO SAY IT ANOTHER TIME. WATCH OUT AND DON'T ****ING DO IT COS IT ****ING ANNOYS ME'.

You should've said this on your mate's face at the gathering.