collectionviewの隙間を埋めたい

お世話になります
uicollectionviewを使っているのですが、iphone6だと隙間が空いてしまい、困っております
http://qiita.com/uro_uro_/items/6e86e6be575e22a6fb20
この辺りを参考にやってるのですが、うまくいかずでして。。。
ちなみにswiftでコードはこちらです

import UIKit

class OtherKodawariVCL: GAViewController {

    @IBOutlet weak var baseview: UIScrollView!
    @IBOutlet weak var kodawariview: UICollectionView!
    weak var delegate: KodawariSearchVCLDelegate!
    var cell_width:CGFloat = 0
    let otherKodawariAry = ["締切間近","登録制","研修なし","平日のみ","4時間以内","交通費支給","主婦・主夫歓迎","高校生歓迎","年齢不問","制服あり","服装自由","髪型・カラー自由","バイク・車通勤OK","大量募集","オープニングスタッフ","紹介予定派遣","駅近","週払い"]

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        var nib  = UINib(nibName: "KodawariCell", bundle:nil)
        self.kodawariview.registerNib(nib, forCellWithReuseIdentifier:"KodawariCell")
        self.kodawariview.reloadData()
        self.baseview.contentSize = CGSize(width: self.baseview.frame.size.width, height:CGFloat(480))
        let kodawari_width = self.kodawariview.frame.size.width
        cell_width = (kodawari_width-CGFloat(50))/2
        var device = UIDevice.currentDevice().model
        println(device)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func closeModal(sender: AnyObject) {
        self.dismissViewControllerAnimated(true, completion: nil)
    }
    @IBAction func decideKodawari(sender: AnyObject) {
        self.dismissViewControllerAnimated(true, completion: {
            self.delegate.doSearch()
        })
    }

    // MARK: - UICollectionViewDelegate Protocol
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell:KodawariCell = collectionView.dequeueReusableCellWithReuseIdentifier("KodawariCell", forIndexPath: indexPath) as! KodawariCell
        cell.check_text.text = otherKodawariAry[indexPath.row]
        //cell.check_image.image = UIImage(named: "icon")


        return cell
    }


//    func collectionView(_ collectionView: UICollectionView,
//        layout collectionViewLayout: UICollectionViewLayout,
//        sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize
//    {
//        
//    }

    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 18;
    }

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */

}

よろしくお願いします。