It's a fairly large room to fill with that sub, but it sounds like you aren't going to be stepping up because of WAF.
Unless you like to punish yourself, you could speed up and increase the accuracy of the frequency response measurement process by using the free
REW software. We know you have a PC and an SPL meter, so you're almost ready to go except for some cables. Give some thought to using it.
Your big problem is certainly the dip in response at ~60Hz and the peak at ~28Hz. Adding gain filters to dips like that isn't the best idea since it eats up headroom. You may not have a lot of that left to bargain with, and dips are usually stubborn. The peaks are easily removed with EQ filters. Disregarding specific levels and assuming the graph is a sub only measurement with an 80Hz crossover used, below is an example target you would shoot for, realizing that the dips are likely going to remain unless you move the sub or listening position.
bass-response-radioshack.jpg
If you're going to continue using the excel method, I would recommend modifying the spreadsheet to use a horizontal axis of 20Hz to 200Hz.....
brucek