Hello Stefanie!
On your website, for example here http://www.stefanie-hoell.com/lissabon/ I can see that you have a 2% rowgutter. If you want even less of course you could set it to 1%.
I am not 100% sure where the problem is. Maybe the rowsgutter seems bigger to you on the website compared to the one in the gridder because it is percentage based. The gridder is narrower than the grid on the website, so the rowgutter is smaller in the gridder. Cause the percentage row gutter sized is based on the width of the grid.
Let's try pixel based rowgutters. Please go to "Lay Options" -> "Gridder Defaults".
Set "Row Gutter in" to px. Set "Row Gutter" to 1
Then at the bottom check "Apply Desktop Gridder Defaults" and click "Save".
Now the rowgutter should be really small.