Mail App Help

On my mail app (using a gmail account) my mailbox headers such as inbox & sub folders etc, seem to be larger than normal.

I have played around with the display - putting it into scaled mode where the entire screen decreases and it seems to be since then that they aren't changing back. I don't want to use the scaled mode because its almost too small but the large headers are so frustrating as I have to scroll to see all my different sub folders, however I never used to have to do this.

Does anyone know how I can change this back