Try something like in this example code. After getting your bbox('all'), do your configure, then adjust the scrollbars.

# add these lines to force scroll to the ends
my @bbox = $can->bbox( 'img'  );
$can->configure(-scrollregion => [@bbox] );
$can->xviewMoveto(1);
$can->yviewMoveto(1);
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See example code in Tk photo pixel colors