Being told to set the network to testnet by lightningd

Console output:

nate@nates-server:~/.lightning$ lightningd lightningd: WARNING: default network changing in 2020: please set network=testnet in config! bcli: Could not connect to bitcoind using bitcoin-cli. Is bitcoind running? Make sure you have bitcoind running and that bitcoin-cli is able to connect to bitcoind. You can verify that your Bitcoin Core installation is ready for use by running: $ bitcoin-cli -testnet echo 'hello world' 2020-08-09T21:22:44.513Z INFO plugin-bcli: Killing plugin: Plugin exited before completing handshake. The Bitcoin backend died. nate@nates-server:~/.lightning$ 

I have checked and bitcoind is running. I followed the instructions on bitcoin.org and used the tar.gz file to install Bitcoin Core. I am trying to follow this guide to set up a Lightning node. I have also checked that the initial block download has completed.

I don't want to run on the testnet, which is what I assume will happen if I change the bitcoin.conf file to set network=testnet, I want to run the node on the mainnet. How can I do this?