File size ballooning from 576KB to 4.1MB when I export from Media Encoder?

Hi I am going stir crazy. 

I have a 8 second video I am trying to render, the original video is 576KB I have rendered it with NO EFFECTS and it comes out at 4.1MB, why is this???

All I want to do is reduce the saturation and a little colour correction then export but I do not want the file to be so enormous can someone help?

I clicked H.264 in the drop down 

This video is for web and devs need it in mp4 

Any help very very appreciated