I Broke My Sister's New Phone By Accident ...Oopsie! ...

So yeah... last week my sister got this brand new phone... it was like shiny and everything... she had been saving up for months to get it too.... So we're hanging out and I'm just playing with it because I love touching the screen and it's so pretty...... But then.... I don't know what happened, but I accidentally dropped it down the stairs when we were running to catch the bus.... It landed on a really hard spot and cracked... she was super upset...... Now every time she looks at me, I see her eyeing my phone too... like maybe thinking about switching with mine which isn't as good as hers was anyway...... She said she won't tell mom because we made a deal once that if something happens to each other's things, it stays between us.... But honestly, I feel so guilty... and now when I see her new case at home sitting on her dresser all empty, it makes me sad too...... So yeah, I'm the asshole here for sure... but how do I fix this without being a bigger one? ...