Worst Mom at the Sandbox

I am not so sure I am a very good sandbox mom. You know, when all the moms have their little kids at the sandbox/playground/baby pool, etc and they are all secretly crossing their fingers that their kid is going to be nice and share and not hit or bite the other kids?
I mean, everyone wants to have the good kid, its pretty much the goal of all moms. I know I don't want to be the mom whose kid takes another kid out for no reason, or keeps snatching someone else's toys. But, the difference is, I also don't want to be the mom who is forcing my kid to share her stuff because little Sally is whining because her mom forgot to pack her Dora doll and now she has nothing to play with.

A few things about me...
I am not great with kids. I mean, kids I like are awesome, but overall I don't have much patience for kids. This fact makes me kind of immature when it comes to dealing with situations that my kid is in...examples to come. And, I am also super protective of "my people", I always have been. Which sometimes makes me say/do things I normally would not say or do.
So, there is a girl named Angelica (not really, but think Rug Rats on Nickelodeon circa 1990's) at daycare. And man, is this kid a piece of work. I really cannot stand her, I know that's wrong because I am an adult and she is just a kid...blah, blah, blah. You mess with my kid, you mess with me. She is kind of a bully and just all around nasty to Elle. Believe me, Elle does not take it sitting down, there were a good few months when the first thing she did when we walked in the door at daycare was push Angelica. (which is wrong, but sometimes made be giggle...I know, I am 5 years old!)
Angelica has a little sister who also goes to Mimi's and Elle loves her. The first thing she does is say hello to the baby when we get there in the morning. Sooooo, the first thing Angelica does is jump up and block Elle from seeing the baby. This morning when Elle walked up to the baby, Angelica came running from the other side of the room and jumped in between Elle and Baby. So I said "Man, Angelica, you are so bossy, you might not have any friends when you get older". See what I mean? I can't help myself, stuff like that just rolls right out, sometimes I don't even realize I am saying it loud enough for other people to hear me. (until I hear Mimi giggling in the next room)
This is what I mean, how am I going to force myself to be sweet like the other moms and chat nicely while crossing my eyes, toes and fingers that my kid doesn't do something mean to another kid. Or worse yet that one of the other kids does something mean to mine and I unknowingly unleash some of my immature/inappropriate comments on an unsuspecting 2 year old.

Man, this parenting stuff is tough.