Is it normal that i am socially awkward?

Sometimes I think that I get confused in certain social situations when I should know what's going on. For instance, today I went to the post office to pick up mail, and I had to go to the window because all of my mail couldn't fit in the box. The lady came to the window with this big box, and when I was done taking the extra mail, I just stood there. It was only like 10 extra seconds. I think I was waiting for her to put the box away or say goodbye or something. But she was talking to a new customer already, so maybe she just expected me to walk away.

Another time, a few years ago, I was at Six Flags with some friends and accidentally walked down the steps with a girl in our group who was on crutches. In other words, I neglected to stay a couple steps behind so that she could get by.

I also realized that I don't always know that some boy I am talking to is trying to hit on me or ask me out.

In general, I think that I don't know the precise time to do things, like end a conversation. I might prematurely/abruptly end a conversation if I sense that the person doesn't want to be talking to me particularly, but sometimes I am wrong and it's awkward.

Am I normal, or do I perhaps have a social disorder?

The main reason this is on my mind is that I was talking to my friend Megan once, and she told me that a boy we both know has a mild social disorder. When I said I didn't notice that about him, she made a "knowing" face to our other friend, as if to imply that I have one too.

P.S. A few people in college used to call me awkward.