http://www.quickandeasywebbuilder.com

Trying to create a basic setup for a new website.
Have now a size challenge on my Kindle. (showing only about 60% of the site)

Default width: 1,366
break: 768
break: 320

Kindle Fire 10 screen size:
Type IPS LCD
Number of colors 16,777,216-color
Diagonal Size (inches) 10.1 inches (71.0% screen-to-body ratio)
Size (mm/in) D (256.5 mm), H (218 mm), W (136 mm)
H (8.56 in), W (5.35 in)
Aspect ratio 16:10
Pixels Per Inch (PPI) 224
Color depth 24 – bit
Resolution 1920 × 1200 px (FHD)

I realize this is a very rookie question, but I do not want to start on the wrong foot.
Do I have to add another breakpoint or might something in the settings not correct?

www.erikslebos.com

I cannot see exactly what you have done based on the published page, but it looks like you have wrongly configured the breakpoints.
Please open 'Manage Breakpoints' and make sure 'Activate breakpoints when browser window is larger than the device width' is selected.

See also the FAQ:
viewtopic.php?f=10&t=43085
(When do I use 'Activate breakpoints when browser window is larger than the device width'?)

That was indeed the cause of the problem. I had noticed this option, thought that the setting was okay but nevertheless should have tried the other setting to be sure before asking. Sorry and thank you very much.