An idea about gravity that isn't correct but is still cool

So, our universe is expanding very quickly. Expanding not in the sense that more matter is being created and adding to the edges of the universe, but rather our universe is stretching like a piece of rubber being stretched in all directions. So, as this rubber is being stretched, each planet gets further and further away from each other planet and the distance between any two points in our galaxy (or universe) is getting larger.

Now, to slightly switch topics, when Einstein came up with the idea that gravity is the curvature of spacetime, his wonderful idea sprouted from the idea that, if a car is constantly accelerating, then the person inside it will feel a constant force from the back of the chair. This force, if the acceleration is 9.8 m/s^2, then would be the same as gravity and, in the absence of earth's gravity, would feel exactly like gravity.

So now, back to the first paragraph, if our universe is constantly expanding, then doesn't that mean that the mass in our universe is expanding, too? We would not be able to measure this- one might say that the density of an object would constantly be going down, but if it is in fact the atoms themselves that are getting larger and larger, we could not measure this and, since we would be growing at the same rate as everything around us, we would seem to be not growing at all. But let's say that the matter below us is growing very, very quickly and we ourselves are growing very, very quickly, then there would be a force exerted by the ground on us, resembling gravity.

No, wait, the expansion of mass has to be accelerating to begin with, just like the accelerating car (we wouldn't feel a force if it was just constantly expanding). http://en.wikipedia.org/wiki/Accelerating_universe

Wow, I swear I didn't read that before I made that last statement.

But, yeah. Probably wrong. Fun to think about, though.