DO NOT LIFT DURING SEATING
Well, I did lift the heat sink to check if the thermal paste is spread evenly.
That can cause microbubbles to form in the paste and ruin the seating. It sounds to me like you used WAAAAY too much paste. The blob you put on it shouldn't be bigger than a grain of rice.
Take off the heatsink, get a nice cotton pad (women's makeup accessories do the job well here, if you have a gf) and 90% isopropyl alcohol (just rubbing alcohol from walgreens or something). Clean off all of the gunk, and the next time you apply it...don't put so much. Remember, a grain of rice is not that big, and neither is the amount of gap between your cpu and heatsink.
Don't lift it up to check how well it's spread. If you absolutely have to do that, after you lift it up clean it off again with the alcohol and pads, then reapply the same amount if you get a satisfactory spread.
Remember that your mounting system will clamp it down far harder than you ever could by just pushing it with your hands, so it should spread over a wider area and more evenly after you clamp it down.