Based on the listing I looked at (Vintage Linen Hand Embroidered tea towel ~ linen cloth cocktail glass #352193500233)

try changing

<table id="TemplateWrapper" class="decobgborder" width="40%" border="0" align="center" cellspacing="0" cellpadding="0">

to

<table id="TemplateWrapper" class="decobgborder" width="80%" border="0" align="center" cellspacing="0" cellpadding="0">

and

<table id="DecoBars" width="400" border="0" align="center" cellspacing="0" cellpadding="0">

to

<table id="DecoBars" width="80%" border="0" align="center" cellspacing="0" cellpadding="0">

or reduce the width to 320.  Provided you don't include images the template should be mobile friendly.  If you start adding images, columns etc it becomes considerably more complex to make it mobile friendly.