It is perfectly fine if the pin is not found. Reaver has a set of pins which it uses to brute-force the WPS Pin and the sometimes the pin of the router is not present in the wordlist. However I would recommend you to try the attack a few more times as Reaver has the tendency to overlook the pin. You can also try the full bruteforce method, but this can take few hours depending on the difficulty of the pin. You can also specify the pin if it is known by using the code
reaver -i wlan0mon -b 60:E3:27:BC:11:84 -c 4 -vvv -K 1 -p (Pin)