I ended up saving it as an .xls file instead (since I needed to open it with that anyways) and changed the code to be

$report->attach(
                Type=>'application/vnd.ms-excel',
                Encoding=> 'base64',
                Path=> "/my/home/"."$out",
                Filename=> "$file"."_fixed.xls"
);
[download]

I feel like it may have been something with the encoding? I'm not sure :\