You say you downloaded but not installed yet correct?
There is always a risk to install games to the internal memory, I've done it heaps of times with no issues, it also depends who you talk to, some say no, some say yes and the rest are on the fence.
When installing to internal memory, as long as the install finishes, there is no power outage, don't remove the sd card, etc.. then it's ok.
Why not just get a usb hard drive and install it to that instead if your worried.