Which case are you using? the DIY case which comes along with the purchase right ?
If it is the DIY case then it should fit in properly.
The open side of the fan should face the heatsink fins. So that the fan will blow air towards the fins making it cool down faster.
Please check this images to understand which side to put the fan opening side
After you fix the fan and the heatsink like shown above. You can close the DIY case like this.
I hope this is helpful to you.