You CAN recover your data and possibly even the partition. Testdisk with photorec can recover most if not all that you lost. Follow the instructions at http://www.cgsecurity.org/
I've used it many times for people who made your mistake. After you've backed up all that you find you can try and recover the lost partition with testdisk, follow the in instructions on their site. Even if the OS is gone because of overwriting your file structure should be back and that will make finding more lost data easier.