Desiree,
If you really want a fish tank that's "full of fish" but you also want the fish to live and thrive longer than a month or two, you really, really need to put those little oscars back into a plastic bag or a pail and drive them back to the pet store.
At 23 or 25, you're old enough to know how to separate the crap advice of a LFS patron from the good advice on the fish forums you've joined.
Take back the Oscars and get something that only grows to be an inch or two long. Get a few if you want.
But understand that you are going to need to make a choice:
1. Let fish die constantly until the tank finally cycles itself in 6 or 8 weeks.
2. Empty half your tank every night and replace with new, clean dechlorinated water every night for 6 or 8 weeks.
Option 2 seems hard, but either way it's a lot of work because with option 1 you're
A. Being cruel
B. Have to drive to the pet store all the time
C. Spend hard earned money to buy more fish
Let me also throw out that there is an option #3.
If you know anyone, ANYONE, with a freshwater aquarium that has been running for several months or longer, you can take a big handful of their gravel and put it in your tank and that will cause your cycle time to decrease to a week, give or take. If you could have one of their used filter pads, to put into your filter, you could cycle your tank even faster. Just be sure to keep the living invisible bacteria wet while you transport it from their house to yours.
But with all of these options, you do have to take the Oscars back. A single one full grown Oscar likes a 75 or 100 gallon tank to himself.