There can be 2 reasons:
- You have a low-resolution monitor on a low spec'ed laptop or an old desktop. The smallest screen you can use with Pro8 is 1366 by 768 but that is squashed. Really you should use 1440 x 900 or greater with the optimal being 1920 x 1080.
- You are using Pro8 with Windows 10 and a high-resolution monitor, what can happen is Windows 10 has tried to optimise a very high-resolution screen so the icons are not too small. The problem is when it makes some parts of the screen bigger, it also makes Pro8 too big. You need to change your scaling as shown here.