I've run into this weird sizing issue for my windows form application when run. Now in the designer the program looks like This1 (can't upload more then 2 links so look in comments). However when I run it from visual studio it looks like This (notice how all the controls are closer together, the picture box is automatically wider and taller & the picturebox in tileset subform is larger).
When built and run outside of Visual Studio from the
take a look at this similar question.
And if it's not to late, consider a change to wpf, it responds much better to the different screens and different resolutions - at least in my opinion and experience.