Hi Mengot,
Her contradictory behavior may be an indication that she is trying to play hard to get.
The first sign of this was when she rejected your initial request for her number, only to give it to you the next day.
Then you write her about how you feel about her and she tells you that she just want to be friends. But, the next morning, she was still staring at you and continues to do so.
One of the most effective ways to get a girl to stop playing hard to get is to take control over the situation.
This starts with ignoring her in class.
Focus on talking to other girls in class.
Make them laugh and give them compliments.
If indeed, she has been trying to play hard to get with you, this type of behavior on your part will make her panic as she realizes that she isn’t the only prize in the class.
If she is truly interested in you, she will start trying really hard to get your attention and may even try to start conversations with you.
In essence, she may suddenly find herself chasing you.