What should I wear to my friends beach/bat-mitzvah party?

I friends having a bat mitzvah beach party! And i have no idea what to wear.... In the invite it said to bring a bathing suit so i thought about bringing this one a href="http://www.shopjustice.com/girls-clothing/swim-sale/striped-pattern-swimsuit/8621314/clearance/1" rel="nofollow"http://www.shopjustice.com/girls-clothin…/a . So i was wondering what acsesories should i wear? And I'm totz confused...Should I come to the party like I'm going to the beach or like I'm going to a regular bat mitzvah (this one isnt my first)? Shes doing it at this place a href="http://www.bereshit-beach.co.il/index.php?option=com_phocagallery&view=category&id=1" rel="nofollow"http://www.bereshit-beach.co.il/index.ph…/a (I'm sorry its in hebrew...I couldnt turn it to english but just look at the pics...) PLEASE HELP!!! First i need to know if i should wear something formal or non-formal and I need to know acsesorise wise and hair wise (i have shoulder length curly hair)! please help! The party is 5 days away (Ooh and i cant call other kids to see what there wearing cuz she doesn't go to my school so i only know a few other kids but i dont have their cell...