When your theme supports wide alignment via add_theme_support('align-wide');, you still have to enable alignment for your block. Replace 'supports' => [ 'align' => false ] with 'supports' => [ 'align' => true ]. Unfortunately, this enables the user to change the alignment, but it does set the default align.
NB: Using 'supports' => [ 'align' => [ 'full' ] ] is not possible at the moment due to a restriction in Gutenberg.
