Screwed arduino bootloader

Hello. I'm having trouble with my arduino. I accidentally tried to upload a program to my arduino uno board, but under Tools>Board I had marked down Arduino Leonardo instead of Uno. I changed it, but it isn't working. I think I may have totally screwed up the bootloader on my arduino. Is there any way to download the correct one? Thanks.

It's unlikely you damaged the bootloader by attempting an upload for the wrong board. It would help to know what you have tried. Have you tried restarting the various pieces starting with cycling the USB cable on up to rebooting the PC?