My first instinct would be to make the regex like this:

$words_to_match = qr/\s*Hello\s+World\s*/;  # use \s* or \s+ as needed

@trials = ("Hello World", "  Hello   World  ", "Hello,World");
for ( @trials ) {
    $result = ( /$words_to_match/ ) ? "matches" : "does not match";
    print "$_ $result\n";
}
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