No offense, but if your friends say you are you most likely are. Instead if trying to convince them you're not, trying changing yourself so you aren't. Ask them what makes you snotty, and ask for honesty, and then work on changing those things. In the end, you and your friends will probably like you better for it.
Hi Maria! This sounds familiar. I always remind my daughter to smile. She is shy so she tends to be quiet and not too friendly which can be misinterpretted as snotty(stuck up). When I'd drop her off at school I'd say the usual " have a good day, love u...and Smile." I'm sure the people that know you know your NOT snotty and love you just the way you are.