Thank you Lordmonkus! The good news is that it's fixed. Still a bit confused about what was going on, but I think I know what may have caused the issue.
After reading what you said, it made sense; the extra command line was creating a conflict. But when leaving it blank didn't work, I deleted my roms and reloaded them.
And walla, it works now. I think the issue was that when I first created the individual NeoGeo platform, I didn't set the proper core. That wasn't covered in the video tutorial.
I loaded the games and when they didn't work, I went back and noticed I missed the core. So even after setting the core, games wouldn't launch.
Now that the core was set, I reloaded the games and that fixed it.
I'll leave this thread up in case someone else runs into similar issues.
Thanks again!