Some more information would be helpful.

First, why reinvent (rewrite) the wheel? (Homework?)

Second, what OS are you on? If *NIX, Net::Ping with ICMP needs root permissions.

Third, have you inspected the actual packets to see if the TTL setting really isn't having any effect? (e.g. Wireshark)

If you could also provide a short, runnable example that demonstrates the problem that would help too.