Well when you are 13 years old and finding what ways to wield power in the world - those 2 girls have certainly found it.
Tell them to ****off in your head. Diminish it to a primary school level prank and ask yourself why that comment mattered so much?
If you allow them to invade your head space so much who is being the primary school student? Unless of course there was some truth to the rumour and it has 'hooked' you in somehow.
Whatever you allow yourself to feel is your responsibility. No one else can control your head or your thought train. You cannot change yesterday, only how you feel about it today. Just be aware when unwanted doubts or thoughts occur, then block them with an image that removes them (imagine them shrinking down like a deflated balloon to nothing)