Screen Error. Big size

I download Shotcut for Linux Mint(Debian).
Almost running but the Buttons are Bigger then normal.

I can not access the bar and edit videos.

←Shotcut Programm in Fullscreen←Normal size Program in Fullscreen

How i can do fix that?

graphic card: NVIDIA GeForce GTX 960
random access memory: 32 GB
OS: Linux Mint 18.2 Cinnamon 64-bit
Cinnamon Version: 3.4.4
Linux kernel: 4.8.0-58-generic
processor: Intel© Core i7-2600 CPU @ 3.40GHz + 8

Sorry for my English. I’m from Germany.

Thanks in Advance.

Tobstr_ / Tobi