lupyo I understand, I ran into this myself. You can do this one of two ways:
Move composer.phar into the folder directly above the flarum folder. Now run:
../composer.phar create-project flarum/flarum . --stability=beta
OR
Create a new directory inside the folder where you have composer.phar. Now run:
composer.phar create-project flarum/flarum newfolder --stability=beta
Replace newfolder with your new folder's name, obviously.
Let me know which one you used and if those work.