How to stop being so awkward?

I swear, I'm the most socially awkward person ever. Well, maybe tenth from last- but still. Somebody will say something as simple as hello and I'm like, "merghermehhehheh, hi, *mumble mumble*" or someone asks me something or I don't know!!! AGH. Its awful! Plus I feel like I have a really awkward voice that sounds like a 9 year old boy or a nasally old person (I'm a 14 year old girl). Its slight insecurity and mainly just my personality. I truthfully think I am a nice person if you know me, maybe a bit sarcastic which can be unintentionally mean, but yeah. Is there away to stop myself from sounding foolish?