Cooling perhaps isn't the best - I think there is one fan in the front but it's covered by a "door" (my case is the Antec P100) and then one to the rear!
My thermal paste application was a bit questionable because the cooler backplate was loose and so I had to hold it on with my left hand while trying to line up the cooler with my right!
It should be fine as long as you used enough thermal paste.
It's been shown to be a myth now that how you apply thermal paste matters. The reality is that as long as there is enough it will spread and cover the IHS. The only bad outcome of using too much is that it might seep out over the edge, which again isn't really a problem (unless you've emptied a whole 20g tube or something).