While D.Kallan focuses with his answer on how to make it closer to Brackeys', this answer focuses more on if you actually should do that.
Since you are new to GameDev, I would guess for now most of your projects are for yourself and the learning experience. Instead of following the tutorial to the letter, you should make the game look great on your own platform. Since the topic of handling different resolutions, fit to the screen and similar can be quite confusing (even more so when you try to learn the basics), you should fix your game to the resolution you are actually using yourself.
That means, if you plan to make a small mobile game, use a fixed aspect and enter your own mobile resolution there. If it is for pc, use your screen resolution under which you plan to play the game later. This saves you the trouble that while the game will work and looks similar to the tutorial in the editor, it might look totally different when you want to play your own game or show it to friends. Once the game is actually done and looks great on your own hardware, you can learn about the topics on how to make it look great for everybody else.
You can set a fixed resolution in the game tab.