So I don't know how to use the PacketBuilder, but I did figure out how to send custom packets.
I first created a byte array with my data in it.
Then used the PcapDotNet.Packets.Packet constructor to create a packet.
new Packet(PacketData, DateTime.Now, DataLinkKind.Ethernet);
Then I with the help from the
GitHub wiki, send the packet from my selected device.