previous audio recording onto new track

Alright, let's start. Please make and post screenshots of Preferences > Audio > Devices tab and your Project's window with the problem track selected and shown in Inspector (left side of Logic's window).

Since you're using iRig and Built-in Microphone as input, my guess is the mic is just picking up the output signal. Which would be consistent with the symptoms you describe. A potential solution would be to solo the current track (or just mute all other tracks in your project) when you're recording guitar, to avoid their output being picked up by the mic (even though you're recording it through iRig).

I'd invest in an external audio interface, if I were you. Also, please take note that when you're recording MIDI, your keyboard transmits, and Logic records, data, not sound. Software instruments then make sound, based on the MIDI data recorded. This is a very important distinction between audio and MIDI.

iRig 2 is not a fully fledged audio interface. It's primarily designed to work with mobile devices, and does not require installation of any drivers. That's why your only option is "Built-in Microphone" when you connect iRig directly to your Mac's built-in audio / headphone jack. macOS' CoreAudio component does not have any other audio drivers / devices to choose from.

Try the following setup:

1) Connect the iRig to your mobile device with some sort of an amp app open (as an iRig user you may download and install AmpliTube app: see instructions on p.6 here https://download.ikmultimedia.com/plugins/Manuals/iRig2/iRig_2_User_Manual.pdf )

2) Hook up iRig's amp output to your Mac using a separate audio cable

If my guess is correct, the signal sent to Logic this way, shouldn't have any mic input mixed with it.