The above image shows what you get after editing and entering the text as seen.
Obviously, follow the tooltip to click the Button when the text is completed and correct.
The binding is set to 'Property Changed' so as to feel more responsive to your editing.
A tooltip on the Image control reminds you to re-size the WPF Form so that any resultant QR code and text is displayed in suitable proportion, and therefore probably better for a mobile phone /device, to read it.
You can keep this handy so you can generate and screen capture any QR code you need to create and use / distribute. I have not sent the solution file as I am using DevExpress assemblies which you most probably don't have. We can sort that out for April 16 - 19 and the 'xBase.Live conference'.
Just had a thought - I will further add a feature to allow a choice of colour as well ;-0)
Have a nice Winter Olympics weekend !