1. if you got the number:
So if you got her number on monday. Good! but don't be calling her or texting her everyday. The way you measure how long you should wait until you call/text her again is by seeing how great of an impression you left with her last. For example if you saw her in school and had a great convo, made her laugh alot, whatever. wait maybe 2 days before you call/text her.
Another thing you could do is not text or call at all until the weekend and since you go to school with her then find a way to come across her in school and game her maybe 3 times in the week then when the weekend comes you give her a call and tell her your going somewhere and that she should tag along or straight up say "your coming on a date with me tomorrow" if you text this dont add in the "LOL" it makes you look scared of her reaction to what you said. i recommend calling instead of texting tho.
2. If you didn't get the number:
If you failed or chickened out on monday. Its alright. Because you guys go to the same school, so she's not gone forever. and yes i do think she liked you when all that staring was going on. You got to learn to act on that man. Don't stop and think so much! Be in control of the situation always, girls love guys that take risks. If you take too long like you did the girl WILL move on. and at this point if she has moved on and doesn't really talk to you or stare at you then this is what you have to do.
A. if she's alone walking - start walking next to her but be a little ahead of her and talk over your shoulder. Have good body language. then say, "Hey Stranger" with a curious smile. practice in front of a mirror first. you don't want to scare her lol. then after she responds don't go with the same shit every other kid would say. be different. Be funny. but do not end up in the friend zone. if you feel you guys are talking like friends then wake up! and realize you have to go into seductive mode.
B. If she's with her friends - go with one of your friends and have him distract the others. or if you feel your up to it go on your own. talk to the friends. win them over. then tell them " you know what ive been talking to all of you and haven't even said a word to her let me borrow her for a sec" the friends will smile or giggle or say "yeah sure". Make sure the target is looking when you say this. then you take her hand without asking permission and pull her away with you else where and go from there.
Make moves. dont wait for another staring contest. Grow balls man trust me your gonna need them

good luck.