Nice scientific rebuttal. I don't think that science is the answer to everything though. The universe in infinite, which humans have a difficult time comprehending, and the earth isn't going to explode. I know that. Nor is the universe going to collapse on itself, or shatter, or blow up or anything. It's bigger than us and it's eternal. These conclusions that science has given us are in some ways just tactics to get us to buy into their ideas - for example is global warming going to cause the next ice age, like it was twenty years ago, or is it going to cause the earth to shrivel up and all life to die, or does global warming even exist? An interesting thought hey? Science can't explain God, but God can explain science. There is also no such thing as anti-matter or immaterial matter. Science can't explain light, how it moves with or without a medium. But we do know something spectacular about light, that it's presence dissipates darkness, and it's absence allows darkness to encroach. I don't believe in either the Big Bang, the Big Crunch, or anything of the like. Seeing that things are ordered must lead to the idea that intelligence ordered it, and no scientist or scientific explanation can go beyond that. From Albert Einstein, one of the most influential scientists in the world (atom bomb for example), One is asked to imagine that one has found a watch on the beach. Does one assume that it was created by a watchmaker, or that it evolved naturally? Of course one assumes a watchmaker. Yet like the watch, the universe is intricate and complex; so, the argument goes, the universe too must have a creator. And one point I'd like to take from your argument, you stated:
...we can't produce energy, however it is still there, we just change it's form.
You're right about that, and we also can't create the elements or destroy them. They always exist in there elemental form. Now you're going to say, "ah, but the Bible states that God created the Earth." and I'm going to tell you that the Hebrew word for 'created' also means 'organized'. And these types of things including law-like structures are eternal. Science can't change that.
Now back to your theory about nebulae not being comparable to planets - why not? Planets are bodies of mass, and so are nebulae. That doesn't change anything. bunch of asteroids floating a way from a planet will behave in the same way as a nebula, not in the same way as a planet. I don't think that gravity really plays much of a role in the universe. We will likely find that gravity, though it exists on the Earth as it does, does not work everywhere in the same way. We will also likely find that other theories made physical laws are not accurate. People like Nikola Tesla and other scientists have proven this, yet we tend to stick with what we can explain, and not what we can't.
So why can't the universe be infinite? Numbers are. They never end. Why does it have to? To satisfy us? So that means that time, although perhaps measurable, is also infinite. What makes our planet so special that we think we know when the universe will end - I don't think it will - it's just another hoax from the scientific community.