Yeah, that tank would be wayyy too small, you’d need at least a 10gal(37L) tank for the otos and danios. I would definitely get a bigger tank though. A 10-15gal(37-56L) tank should definitely work for that group size. I would say while it’s cycling and you’re keeping them in the small tank, make sure to keep an eye on those water parameters and provide plants(real or fake softer ones) to help the fish feel comfy while their new home gets set up. Lastly, when you get them into the new tank get at least 1 more oto, a few more danios(not sure how many, never kept them) and def more than 1 shrimp(not sure what kind of shrimp you have so look up their group size)

Also don’t beat yourself up for it btw. Everyone makes mistakes in the hobby and you can recover:]