Excellent! Because stars are made up of plasma, most sources list plasma as the most abundant form of matter, making up about 98% of the known matter in the universe.
There are some sources that classify plasma as a type of gas, in which case gas would make up most of the universe.

You may also find sources that talk about Dark Matter, matter that we cannot detect. Some scientists speculate that the kinds of matter that we know of (solids, liquids, gases, plasmas, Bose-Einstein Condensates, etc.) only make up about 25% of the total matter.

Why would scientists think that there is so much matter that we can't detect? The planet Neptune was discovered by noticing its gravitational pull on the other planets, even before anyone had seen it. Scientists use the same idea to speculate about dark matter because the movement of stars and galaxies seem to indicate much more gravitational pull than can be currently explained by the matter that we can detect. The source of this "mystery gravity" has been dubbed dark matter, at least until we find a way to detect it, or explain things in a different way.