You're math is correct but you've left a few things out.
First, you set up the problem so that you're considering the moon at opposition (i.e. to get the moon-sun distance you're adding the moon-Earth distance to the Earth-sun distance). So what if the force attracting the moon to the sun is stronger? The Earth is "in the way", so when the moon falls towards the sun, it's falling towards the Earth as well.
More interesting to consider is what happens at conjunction, when the moon is directly between the Earth and the sun. At that moment the Earth and moon are travelling in parallel directions. Which way the moon goes from there would seem to depend on who wins out -- Earth or sun -- in the gravitational tug-o-war.
Next: probably you should not be talking about gravitational force, but acceleration.
So, acceleration of moon towards sun at conjunction:
Ams = 0.8933634046 x10^14.
Acceleration of the moon towards the Earth:
Ame = 0.4042680134 x10^14.
(NB: I don't include units because I never multiplied by the gravitational constant... you can just pretend it's there, and treat these values as constant coefficients.)
Yes, Ams > Ame. In fact, Ams ~ 2Ame. So why doesn't the moon fall towards the sun?
Well, it is! But what you forgot to calculate is the force with which the Earth is pulled towards the sun, and hence, the acceleration of the Earth towards the sun. As it turns out, Aes = 0.8887782751 x10^14, almost enough to completely cancel out the rate at which the moon falls. The discrepancy is more than made up for by the 0.404 x10^14 moon-Earth acceleration. What's happening is the Earth and moon are both being pulled towards the sun at almost identical rates, and the Earth gives a comparable (though smaller) tug on the moon in the opposite direction, which keeps the moon in orbit around the Earth.
To consider an analogy, imagine dropping a magnet and a small piece of iron off the roof of a tall building, at the same time, one an inch above the other. The magnet will still attract the iron on the way down, even if the magnetic pull on the iron is much less than the gravitional pull of the Earth on the iron.
Basically, the Earth isn't trying to keep the moon away from the sun. They're falling down together, and the Earth is doing a little bit on its own on the way down.
-Erasmus