You have a Media Queries for a specific screen size, this may fix something but is not the best way to cover the responsive design, maybe you need back on your code and check change font size’s for em,rem and use percentages and relative measure.
In fact, if your design maybe not work as you expect try to read about mobile first design and progressive enhancement.
A tip is normally media queries comes from less to more (from 0 to 400px, from 400 to 768px, …)
If you are from México maybe I explain to you in spanish.
