Hey Brian2, welcome to the forum.
As mentioned above, the 3g won't work for anything except ONE betta fish (or maybe a couple endlers or shrimp). If you are committed to keeping fish and want some flexibility with what you can have, you might want to consider getting a 10g or larger - the larger the better, actually.
Even if you do stick with the 3g and one betta, you still need to 'commit' to learning about your fish's needs and put in some effort to keep the environment properly maintained for your fish's health. Otherwise you will experience lots of frustration and dead fish. No fun.
So, do you have room/money/desire for a bigger tank? If not, take all four of your fish back to your store right away, and we'll gladly give you advice on how to get set up for a lovely small betta tank.
PS - the reason your water is cloudy is likely a bacteria bloom from having too many fish in that small a tank, without the tank being properly cycled. It won't just clear up, sorry.