So embarassed right now!!! What should I do?

Ugh, I am SOO embarrassed right now..:( My brother who is a senior brought his girlfriend of 2 years who also goes to my school, over to my house. I'm super shy when it comes to people like my older brother's friends or just people I don't really know in general. So my bro and his girlfriend went and sat in my living room while I was in the kitchen. Then my mom walked into the living room and sat and talked to them as well. I was in the kitchen the whole time eating pizza lol, then I finally came out to the living room and I'm just like "HIII!!!!" and plus I had like pizza in my mouth -__- and his gf is just like "oh uh.. hi..." and my mom gave me like a "WTF" kinda look. I was all awkward and had food in my mouth and just came outta the blue all like "HI!!!" and I had never really talked to her before. Btw I'm a freshman in high school. and Idk I'm just uber embarassed :/ What should I do to not worry about it so much? :S Thanks. :p