I cant locate my Sandbox site

Hi, i have been working for a few hours updating a theme template in sandbox mode, i then tried to install an under construction plugin on my actual site so that i could try and activate the sandbox copy to the domain name and now when i open sandbox plugin there is no evidence of my site i have been working on and i just get the message

function WP_List_Table::get_columns() must be over-ridden in a sub-class

Is there any way of retrieving this that anyone knows of? My last back up would have been yesterday so im wondering if i can save all of todays work?

Thankyou! Steph