Press P and check your discoveries !
Your first planet should be there in that list on the far left side. Systems /Planets discovered.
Whether or not you'll find it on that terrible map is anyones guess.
🙂
That part I know. However, I am talking about finding it on the map. I know if you pick a random solar system, you can hit F to set a waypoint. What I'm looking for, or REALLY wishing there was, was a way to either set a waypoint from the Systems/Planets tab, or, a way to see the lines on the Galaxy Map that will show me the visited Solar Systems.