First lesson you should learn from this is to plan ahead. I've helped many people build computers and most of them have always answered "No, I won't be gaming" when I ask. Then sometime later I hear from them "The computer doesn't work, what's wrong with it" and I ask what is going on and they say "Well, I tried to install this game...".
It costs you more to buy without pre-planning. That said, I'd get a new case. That's not a gaming case. You want good airflow for one thing, you want room for a decent power supply as well as the videocard itself. You might eventually need to, or want to, add more cooling components. This case was made to be sleek and take up little space- not a priority in gaming.