dont be too hard on yourself, it happens.
If I were you, I'd return the dwarf gouramis because even though they seem fine right now, they will become aggressive toward eachother as they mature. Also, from what I've heard, SAE
's will definitely outgrow your tank, but you have a while. So if you don't want to return any fish, and have a bit of money to spare, you can always pick up a second tank. However, if that isn't an options, otos are a good replacement for SAE
's but they should only be introduced to a tank that has been established for a while because they can be very sensative.