@Stephanie *****
I guess I don't know the details. You made it seem like you were already in Thailand. If you're waiting for the ED visa to be processed as an e-visa online because you applied when you were out of Thailand, there's no problem leaving and returning on it if it's issued once you already entered Thailand.
If you are applying for the ED visa inside of Thailand, there's no way to receive it if you're outside of Thailand since the immigration office needs to stamp it into the passport.