No need for a negative look-behind.

while(<DATA>){
    chomp;
    print;
    print /^[^?]*<<\w+>>/ ? " - Match\n" : " - No Match\n";
}

__DATA__
http://www.google.com/?stuff=<<merge>>
http://<<merge>>.place.com/?blah=blahblah
[download]

prints

http://www.google.com/?stuff=<<merge>> - No Match
http://<<merge>>.place.com/?blah=blahblah - Match