You don't need two accounts, people on Mastodon can follow accounts from PixelFed and vice versa.
People can't find your PF account because the address you have written is incomplete, it doesn't say the name of your server. Your full Pixelfed address should look something like @ (username) @ (server)
If you share the full address with people on Mastodon, they will be able to follow this full address by pasting it into the search box.