Hi, 

While doing a trailhead challange " Improve Your Classic App by Moving It to Lightning Experience' -'Set Up Your Salesforce Org " ,  I changed my trailhead playground site name, now I am not able to access that playground, User name for that playground is "curious-raccoon-15151.com"
I've many uncomplete modules and important code in that, please help me so that i can get acess to my org.

Thanks,
Kirtish