Yes, it's sent.
It will stay in your outbox until the receiver chooses to open it. They may or may not, it's up to them. They can also delete it unopened.
New members are probably less likely to get PM responses in their early days here because many established members seem to prefer to get to know newbies from their posts built up over time before engaging in PM dialogues.
This and other questions are answered in the Frequently Asked Questions section on this forum.