I told this girl I like her and her response was 'thank you :) <3'?

i think you should. but first try to hang out with her alone for a while and if you guys get along well go for it.:D her response means she most likely likes you because i know from experience if someone a girl doesn't like tells them they are beautiful i usually just say thanks never a smiley and defiantly no heart so she likes you..... thats the best i can come up with i hope that made sense