You will notice that the Linux partition is file system ext4 and the others are ntfs. Sda3 is an extended partition containing sda5 (set up originally when I had just Windows 7 and is where I keep my datafiles) and sda6 which I created later to hold the Linux operating system (originally Lubuntu18.04 but changed to LM19.3 later upgraded to LM20) Sda2 is the Windows partition which contains the operating system files and installed Windows programs. It existed before LM20 was installed and I ran Windows 7 alone but now it will contain the grub file for the dual boot arrangement. Sda1 is the system reserved partition containing the boot information. My internal hdd is divided into 4 partitions: sda1, sda2, sda5 and sda6. I have a dual boot arrangement with LM20 and Windows 7. You may see something a bit like my attached png image. What do you see if you boot from the USB device and run Gparted - are your original partitions recognised? You should also be able to rescue your personal datafiles using the USB device even if you do decide to ditch Windows. However, you may not have 'screwed' your system irrevocably. Boot from your USB device and open the 'Install Mint' file on the desktop upper left. If you are really happy to ditch Windows and your datafiles, installing Linux Mint to replace them should not be a problem.

How to format my hard drive on linux