Stay fast to what you want. We had just a Maid of Honor and a Best Man. That's it. We did included our immediate family as part of our procession - and were told my the priest that more weddings should be like ours. We didn't do it for what it would look like, but because it was meaningful to us. Just like you!
Since your mom invited people, tell her its her responsiblity to uninvite them b/c they are not invited. What she did was very disrespectful to you and it is not your problem to solve. If you don't hold fast now, chances are she'll do stuff like this again and you'll spend all your time battling with her. NOT a good use of your energy.