iOS PDFKit not filling UIView

I'm using PDFKit to display simple PDF's. When I display them on the screen inside a UIView, I've used the code below.

Aims: - Start off with the content to fill the view (conforming to aspect ratio) - Not to get bigger than x4 on zooming - Never to get smaller than screen fill size

override func viewDidLoad() {
    super.viewDidLoad()

    if let path = Bundle.main.path(forResource: "Disclaimer", ofType: "pdf") {
        let url = URL(fileURLWithPath: path)
        if let pdfDocument = PDFDocument(url: url) {

            pdfView.document = pdfDocument
            pdfView.autoScales = true
            pdfView.maxScaleFactor = 4.0
            pdfView.minScaleFactor = pdfView.scaleFactorForSizeToFit
            pdfView.displayMode = .singlePageContinuous
            pdfView.displaysPageBreaks = false


        }
    }


    self.view.backgroundColor = UIColor.black
}

In storyboard I have set a constraint for UIview to fill full width of the screen - which it does.

Now while most of this works, the original size of the PDF in the UIView is smaller than the UIView. There is a margin around the PDF. I can zoom in and make he Pdf fill the whole screen, before it overflows and scroll bars come into play.

I can't seem to work out how to make the PDF fill the UIView fully. I've tried using .aspectFill but this doesn't change anything. Interestingly, if I make autoScale = false, then the PDF starts off 2x as big as the screen

Would appreciate some help. Thanks in advance

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