Okay, first things first. The white space beneath the image in the background is quite distracting for me, I feel like it would look better if there was a matching black colour to make it more seamless. There is also not enough spacing between each paragraph, making it look all clumped together.
"The day started as a typical day for a teenage girl. My mother..." I'm not sure I like how this started, to be honest. It feels awkward considering the rest of the story seems to be in first person. Maybe replace "a teenage girl" with "me". I understand that you're likely trying to get the protagonist's age across from the get-go, but it could be incorporated into the story through other means. The fact that she's living with her parents suggests her age.
After the first part of the chapter it goes straight to a couple boys, but the main character is referred to in third person. This feels odd for me, and I think that it could begin with the boys as a prologue, then go into the first person with Sandra. She could then think back to the party and whatnot, and I think that would feel better.
Other than that, the first chapter is pretty good and I would like to subscribe to read more. It's a pretty good read. :)