It's okay. They did tell me to submit more in the future, so that's encouraging. Maybe I'll try Pseudopod, though I don't know how frequently they take flash stories. If you have any suggestions of where to submit a flash fiction horror story, please post a comment!
Submissions to date: 2
ETA: As it turns out, Pseudopod does accept flash stories. I'll try them and search around for other possibilities. http://pseudopod.org/guidelines/