Regex in C - pattern matches too early and drops trailing character(s) - c

Question

I'm working on an interpolation module in C. I have access to both POSIX and PCRE2 regex parsers. Essentially, I have a block of text which contains tokens. These tokens are substituted with values from a lookup table. Each token has the ability to specify alternate text if said token is not found in the lookup table.
Nominally, a token is formatted as ?{token} To handle situations where a token may not be defined and you want alternate text, you suffix the token with a ':' (color) and the alternate, thusly ?{token:alternate} The alternate can be plain text or another token.
The module has the ability to process nested tokens; this includes a token as alternate text. Such a definition looks like ?{token:?{alt_token}} And herein lies the problem. When I parse this, I get ?{token:?{alt_token} as the match. Notice that the closing '}' is missing. When I un-greedy the pattern where it captures the alternate text, the regex over-grabs.
A pathological example would be ?{some:?{deep:?{replacement:?{inside:all this}}}} Ideally, this would grab and resolve (on each pass) the following:
?{inside:all this}
?{replacement:?{inside:all this}}
?{deep:?{replacement:?{inside:all this}}}
?{some:?{deep:?{replacement:?{inside:all this}}}}
... but what I get is each one missing its closing '}'
I'm using several capture groups in my regex to group/grab the token and its optional alternate text. Here's my regex:
`"\\Q?{\\E([\\Q:=\\E]{0,1}[A-Za-z_-][0-9A-Za-z_\\.-]*?)(\\:(.*?)){0,1}\\Q}\\E"`
match[0] is the whole RE; match[1] is the token; match[3] is the alternate text
Any suggestions how I might modify my regex to retain the closing '}' when the token to parse ends with more than one '}' ... ?