How do you know if other girls are jealous of you?

Here it is... It might be long + I tend to go off track so bare with me! Ok so I'm 16 just started a new 6th form it's really good education wise and I know some people there so Im not alone lol.. Well not to brag.. I do dress well as in i buy the latest trends e.g jordans, designer bags, true religions etc.. and I'm quite pretty ok enough about me coz I really hate sounding vain.. But anyways 6th form you can wear anything but jeans, so People can get dressed up instead of wearing a blazer or whatever.. So today we was in some hall with all the year12s and we had to sit in groups, next to our table there were these two girls who are gorgeous, very pretty girls! And they kept staring at me I could see them from the corner of my eyes so I turned and smiled then they gave me the dirtiest looks and kissed there teeth so I looked away.. Then as we're doing activities which involved all of us moving around getting to know people etc.. They barged passed me even though there was space, so I sat back down and went on my phone.. And some boy asked me are you ok but I said I was fine.. Then after me and the boy became friends we started talking and making jokes.. Later on we had another acitivity Which involved groups getting up in front of everyone presenting their product, so my group went up and I saw the girls looking at me whispering and laughing I just ignored them. Anyways it was there turn and they went up with "the boy who asked me if I was ok" group and they started flirting with him infront of me trying to make me jealous even though i dont fancy him (he is very sexy btw not going to lie hahaha) but I like someone else. But the thing is I don't get these girls problem I don't know them! Never seen them before in my life, so why are they out to get me. I've been nothing but nice and they still treat me like sh*t this is my first day and I Wana move becoz I have a feeling there gonna make my life hell if I stay there.. What should I do? Are they jealous?