you're exporting at 300 dpi. export 72 dpi.
if you make a 100x100 px image in illustrator, you're actually making an image that is 100x100 points. points are a unit with a specific size. if you export a raster image 300 dpi, illustrator is making your image 4.17x larger (300/72) as it's cramming pixels into an already-defined area.