First :welcome: to AC! We are a community that wants to help.
Second, as you have already been given advise on, the stock in your tank is way too much for a 20 gal tank.
Third, if you are willing to take the advise of the many people who have vast experience with fish keeping, we can make your tank an enjoyable one for you and the inhabitants that you ultimately choose for your 20 gal tank.
If you want to keep all of the fish you have, you indeed are going to need a 100+ gal tank to house the pleco/ algae eater, Jack Dempseys, shark and silver dollars (which you will want to increase in numbers to about 6 as they like to school). You will need another 55 or 75 gal tank to house the 3 kissing gourami and possibly the catfish. Yet another tank to house the Angelfish or frogs. The angel by itself could stay in the 20 or the frogs. Not both. If you choose to go this route, we can help you round out the inhabitants of each tank.
However, if you only want the one 20 gal tank, I suggest you return the fish and frogs to the store and start over.
And finally, please, please, research size and compatibility of all inhabitants before you purchase.
haha i did the same thing except not with cichlids
