I feel embarrassed or weird singing in front of others?

I'm not a musician or anything close, but I do like to play acoustic guitar something mostly by myself. I've played for a friend of mine before but really no one else.  I'm planning on taking a small trip in june up to this lake, with a 3 friends. My one friend suggested I bring my guitar with me.  2 of the friends have never heard me play before and I feel a bit odd about it.

I'm not what you would call great but I'm not awful, in terms of playing, singing Id say mediocre.  How do I overcome this fear?