I just purchased and set up my gallery and have discovered the same problem. My gallery is set up as 3 columns and looks fine at desktop or larger pad sizes. However, when viewed on smaller devices like a phone it does not change to a single column and remains at three columns which makes the images look too small.
I saw this post and decided to try the solution before posting here but it did not work properly.
After making the changes, the gallery is now responsive with the images moving into one column on a phone sized screen but they are now only taking up 50% of the width of the screen. The other 50% of the screen is blank down the right hand side! Please see image attached which shows how it now looks after replacing the code as suggested.
Can you offer a solution to this? As it is I cannot use the extension like this.
Thanks
Jon