lately there has been something on my mind im a 13 year old female, one of my best friend ...

That sounds tricky. Maybe you can still talk to them about it. Tell them that it really flatters you but you dont feel the same way but you preffer them as friends. That you enjoy being with them but cant give back such deep feelings
There is nothing much yku cant do if you dont have the same sexual prefference. It was a dumb advice to pretend you have feelings for her because it would put A LOT pressure on you and its like playing house....fake
Tell them you like them as friends.

Well, nothing wrong with reject someone you're not in love with. If she is your friend, you should be gentle, but direct, say that you don't like girls and you only see her as friend. Don't need to be harsh (unless, she is being a bitch with you or violent, don't seems to be that case), I feel kind of sad when someone confess to me and I don't have feelings for the person, but that's normal, one day, you will confess to someone and get reject too. It's normal.

Nothing wrong with not being able to return the feelings, and honestly it's kinda fucked up that your friend was that persistent after you rejected her the first time. If I ask someone out and they said they weren't interested, whether I still have feelings for them or not, I'm gonna respect their response. And your friends are fucked up too, it's a dick move to fake feelings for someone and to try to make you do something you're clearly not interested in? Get better friends ma, shit ain't right.

damn, you did good not faking your feelings. if i was in love with you, i would be grateful even when i confessed to you you still liked me. there are people that would be grossed out, and honestly, if you would try to pretend a relationship with me, i would be sad and mad at the same time. i dont know what kind of friend had told you this, but looking from their perspective, if must have seemed kinda hard to see both of your friends being uncomfortable with each other, but that still doesnt make their decision better. and i think that the 2nd friend may have confessed to you just to try if you would say 'no
or 'yes' to test if you just didnt like the first friend, maybe you were fine with anyone but her, or if you werent lying. but since i dont know any of you personally i cant assume, but i think you did right. if you still think and you feel bad about rejecting them harashly, try to apologize for being rude, but still make them keep in mind you have no romantic feelings for them.