insert PRINT PAGE button after Page/Dom has loaded

We have a site built on DUDA and in the product detail page the client now wants a "PRINT PAGE" button added to the layout however we do not have direct template editing available with the DUDA shop so will need to inject the html into the DOM after the page has loaded. I have personally put cobbled together some script that achieves the html insertion when in the JSFiddle environment but it does not seem to fire correctly when put into the actual page so I think there needs to be some work done around when the script actions/fires. It is obviously not a huge job but definitely needs some script finessing to make it work. You can see the fiddle here: [login to view URL] And an actual live product page here: [login to view URL] We'd like you to have a look at the current coding and put forward a proposal to revise the script to achieve the desired result shown in the attached image mockup. Look forward to receiving your proposals - if you have any questions please ask