with it only being a week old, as long as its clean (red in color), is ATF+4 and does not smell burnt or anything you should be ok. I usually recommend new fluid when someone asks about reusing because there are some that will reuse old,dirty fluid and wonder why there trans wont shift or work properly.

just for reference when i did mine last (Full drain dry) it took me 8 1/2 qts to show full.. Just draining the pan its close to 5.