Using Guided Template language with Ampscript

I am using GTL with Ampscript to personalise an SMS by creating the task activity in Journey Builder which then talks to Salesforce data and triggers a SMS. I have used the description field to insert the SMS message.

This is what I did as per the instructions here

{{=Uppercase(Event."SalesforceObj8e3ec1484b"."Contact:FirstName")}}, message here

And I receive this as an SMS

""=Uppercase(Event."SalesforceObj8e3ec1484b"."Contact:FirstName")"", message here

It is basically replacing the curly braces with quotes. Did somebody had this problem? Do we have a work around on this?