ChartJS - convert 'foreach' query data to JSON

Question

So I'm working on quite a big school project and our goal is to show the presence or absence of all students at our school, we have to show this data using chartJS, now we made a query which selects all classes and a foreach-loop runs through the classes and the the query to select the presence and convert it to JSON, I've been working on this function for quite a few days but I just can't seem to make it work...

Here is my QueryManager which activates the query:

public function getAanwezigheid($klassen){
    $result = $this->dbconn->query("SELECT klas.code klas, ROUND(
(
    SELECT Count(aanwezigheid) 
    FROM aanwezigheid 
    JOIN college ON aanwezigheid.Ccode = college.code  
    JOIN klas ON college.Kcode = klas.code
    WHERE klas.code = '".$klassen."' AND vak.code = 'WFHBOICT.M032.16' AND college.college = '8'
    AND aanwezigheid = '1'
) 
/
(
    SELECT Count(aanwezigheid) 
    FROM aanwezigheid 
    JOIN college ON aanwezigheid.Ccode = college.code  
    JOIN klas ON college.Kcode = klas.code
    WHERE klas.code = '".$klassen."' AND vak.code = 'WFHBOICT.M032.16' AND college.college = '8'
) 
* 100)
    as percentage
FROM aanwezigheid 
JOIN college ON aanwezigheid.Ccode = college.code 
JOIN klas ON college.Kcode = klas.code 
JOIN vak ON college.Vcode = vak.code 
WHERE klas.code = '".$klassen."' AND vak.code = 'WFHBOICT.M032.16' AND college.college = '8'
GROUP BY klas.code");
    $data = array();
    foreach ($result as $row) {
    $data[] = $row;
    }
    print json_encode($data);
}

Here is the code which gets the query(the unserialize gets all classes which are available which are class A-F):

if($_GET['action']=='getAanwezigheid'){
    header('Content-Type: application/json');
    $klas = unserialize($_SESSION['klas']);

    /*This loop runs the query for every class which has been found (A-F)*/
    foreach($klas as $klas){
    $klassen = $klas->getCode();
    $result = $q->getAanwezigheid($klassen); 
    }
}

Here is the result I get:

[][][{"klas":"WFHBOICT.V1C","percentage":"38"}][][][{"klas":"WFHBOICT.V1F","percentage":"67"}]

And I want the result to be this:

[{"klas":"WFHBOICT.V1C","percentage":"38"},{"klas":"WFHBOICT.V1F","percentage":"67"}]

Now I get why I get all the brackets, it's because I loop through data[] every class too, but that's what I'm stuck at. I just need to print 1 JSON result

Any help would be really appreciated.