Thanks for reaching out to us. In order to print at 60 x 40cm at 300DPI, since this is equivalent to 23.6 x 15.7 inches, you’ll need an image of dimensions 7080 x 4710. This is larger than what Ribbet currently supports and so you won’t be able to achieve the full 300DPI.
You could however still achieve this by opening the Constraints dropdown when creating your collage (on the left within the collage settings), selecting Custom… and entering 6 x 4. This will create a collage of dimensions 2880 x 1920, which when printed at 60 x 40cm will be approximately 122DPI. You may still find this acceptable – it will still be pretty sharp.
Note the image file will still say “96dpi” but this is meaningless as DPI only takes on meaning when applied to a particular print size. It can be calculated by print length / image pixel length (in this case 2880 / 23.6″ = 122DPI).
With 1/4 of the image being cropped by your printing software, I really am unsure what the exact issue is here, but if you email us some screenshots and an explanation to support [at] ribbet.com we’ll gladly help.
Let us know if you have any questions!
Regards – The Ribbet Team