3-column gallery changing into 2-column on mobile

hi,

i've recently built my portfolio and there are some things that i can't perfect on my own.

i have 3 columns of pictures in the gallery on my main page but once you check the mobile, there are only 2 columns which leaves one odd picture at the end and in general gives a worse visual pairing than the desktop version.

any way i can fix that with css?

this is my page: https://patrycjahelenabielawska.squarespace.com/

thank you!

i wanted to avoid adding extra pictures as i feel like this amount is just right to capture the essence and grouping these pictures in twos instead of threes alters the overall perception. but you make a good point that threes would be too small for a mobile screen, and definitely scrolling through 2 images at a time is better than scrolling through one. 

thank you for the input and giving me a fresh perspective. i will add extra row to compromise 

☺️