Yeah, I would have to agree, I think you are overstocked too. I would not keep a betta with another FISH, in anything smaller than a 10G. For your tank, maybe a few small shrimp, if they dont get eaten, and / or a small mystery or apple snail or two, and that would be IT. Remember, general rule of thumb is 1" of linear fish per gallon of water. The Betta and a few small shrimp and / or a small snail or two would be about the extent of the bio load you would want to put on a 3G. I have a 2.5G betta tank, and the only other things that would go in there with him ever are a couple of shrimp, or snails.
I guess if your set up is working for you, thats great, but you really will need to keep a close eye on the fish, and espeically on your water quality readings / parameters. Also, Betta's are very soliatary fish, and usually dont like tank mates of the fishy kind.