It's because the images can't fit inside the column anymore so they stack. If you shrink them so they will fit, please note that the text inside your image will also shrink so it might be hard to read. Regretfully, that is the layout offered in the theme for now.
It's technically possible to achieve but his would need custom CSS Flexbox and/or Media Queries which could easily get quite complex.
To widen the gaps, you will need to use the margin controls of each Image element. Please give us a screenshot of the overlap so we could understand the issue better.
Alternatively, you can either use The Grid or Essential Grid for this use case. Both plugins offer responsive column layouts so you can have 4 column on desktop and 2 on mobile and it won't stack. For more details and usage instructions, please check the links below: