If you have trouble pulling manes, definitely recommend using a Solo Comb. They are relatively inexpensive and they only pull select hairs, so for someone who is inexperienced or a horse that is sensitive, it's less of a pulling action and more of a cutting action...
Depending how short it is now, you might still be able to fix it by using the Solo Comb or have someone help you pull it normally. Do not use scissors unless you're working on a fjord, and even then, you have to be careful and use a steady hand. Believe it or not, there is a certain way to hold scissors that makes it easier to cut evenly.
OTTB - I just tried to describe how to do it, but it is really difficult without you seeing it. Let me see if I can find a youtube video(If I can access it). Get back to you in a bit.
Yvw OTTB - Don't ever be afraid to ask questions, everyone's got to learn. Are the people at your barn snooty?? I would hate to ask snooty people is why I wondered LOL