We are constantly releasing materials such as gases and sattelites into space, surely it would eventually fill up with them. Even if it won't, if we increased the amount of materials we released into space to an amount that was at a faster rate than the rate that the universe is expanding, would it fill up?

We couldn't possibly fill space with materials from the Earth.  The maximum amount of material we could possibly release from the Earth would be the entire mass of the planet, including the oceans and atmosphere and the core etc.  Space is vast - the observable universe is a sphere of something like 14 billion light years radius. 

Earth orbit, in particular low Earth orbit, is filling up quickly however.  Satellites, space junk, particles of dust and paint, lost space-tools and so on mean that it's increasingly dangerous up there.  How this could be solved is a matter of debate and to my knowledge no practical solution has been found yet.