You can try adjusting the text size of entire note by holding ctrl and rolling the mouse wheel back and forth. I’m assuming you are using the default theme; but, if not, you can always go into the Appearance section of the settings and change your theme to one that has headings in a size that you like. Another option is to use a css snippet to control this "How to achieve" CSS code snippets. Or you could utilize a plugin that controls styling. I hope this helps get you on the right path to finding a solution. Good luck!