New 5 gallon tank, put betta and 4 fish(plus crab) in, Aggressive betta?

[Puppy&KittenLover]

Well last night i got a 5 gallon, I had my betta but i wanted more fish. So I got a black goldfish, catfish and another one from my other tank which wasnt getting along with the other fish. Earlier my catfished died of sickness(Noticed it was when i bought her, something wasnt right when i saw her in walmart). But I saw some missing scales on my goldfish so i took my crab out and moved her into my 10 gallon with the male crab(hoping to mate them) But I saw my betta attack the two remaining fish very aggressive like. What should i do? I bought my tank for my betta and I dont want to take him out
Just took another fish out due to my aggressive betta