So i convert html page to pdf by using onclick event

My code is:-

function generatePDF() {
    var element = document.getElementById('invoice');

    var doc = {
        filename:     'myfile.pdf',
        image:        { type: 'jpeg', quality: 1 },
        html2canvas:  { dpi:192, letterRendering : true, scale: 2,  text Align: 'center', },
        jsPDF:        { unit: 'pt', format: 'letter', orientation: 'portrait', format: 'a4' },
    };

    html2pdf().set(doc).from(element).save();
}

By using onclick event the page will be downloaded successfully but the alignment of the content is changed. I want to give fix size so the content alignment is not change and also in mobile view the page will be downloaded at that defined fix size.