Push an array into another array inside underscore's forEach in js/node

I have this function to get some data from the internet:

function GetData(callback) {
    var data = [
        ["username", "password", "email"]//Header values
    ];

    doc.getInfo(function (err, sheet_info) {  //the doc is an google spreadsheet object
         sheet_info.worksheets[0].getRows(function(err, rows) {
              _.forEach(rows, function(row) {
                data.push([row.name, row.password, row.email]);
     } );
    });

});



    callback(data);
}

But when i try to use this function:

GetData(function (data) {
    console.log(data) //Has only first initial values  ["username", "password", "email"]
});

Any idea what might be the problem ?