500 MB hard drive only has 300 GB now?

Yesterday while I was going through the process of installing Windows on a partition I had created in Boot Camp, I realized that I wanted to decrypt my hard drive first before it installed, to avoid any potential complications. So I quit before it installed, booted normally, formatted the flash drive I was using and deleted the Boot Camp partition so that I could decrypt and start from scratch again. The problem is, now "Macintosh HD" in Disk Utility is showing 299.25 GB, and there's something else that just appeared called "APPLE HDD HTS545050A7E362" that has 500.11 GB, but 499.9 GB is used. Those are the only two things that are there except for my USB drives, and I really don't understand what any of this means and want to know where the 200 GB (how much I partitioned for Windows in the first place) went. I've heard people say to just "reinstall Mac OS" but I have a lot of stuff on my Mac, a really slow connection (took 3 hours to download the Windows ISO), and I really hope that there's a better fix.