Concentration and volumes
The concentration is defined as the amount of particles per unit volume. If you have a greater concentration of sulfuric acid, there are more sulfuric acid 'particles' ready to collide and react with the calcium carbonate particles. This is a simple result from the collision theory of chemical reactions.

So, increasing the concentration of the sulfuric acid should increase the amount of carbon dioxide (and other products). However, this is not always the case.

Consider the case where calcium carbonate is the limiting reagent/reactant. This basically means that all of it gets used up before the other reactant gets used up. In a case like this, increasing the sulfuric acid concentration will not affect the amount of products, simply because there's not enough calcium carbonate. 

It's like asking if having more flour is going to help you bake more cake. Often, it does. But if you don't have enough of the other ingredients, it doesn't matter how much flour you have! Obviously, this is an incomplete analogy because you could probably still make a cake, albeit a nasty one.