No, actually the following should work just fine:
"{{([^}]*)}}"
Edit:
As pointed out by dtb the expression above fails for a string containing a single }
within the double brackets. To handle this case the following example would do a much better job:
"{{((?:}(?!})|[^}])*)}}"
Edit 2: The simplest solution however would probably be the following:
"{{(.*?)}}"
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