I just got a major lag spike for 20 minutes and even though it kept saying "Reconnecting" I got "Leaver." I dont want to get banned, is there anything I can do to inform Riot or something?

Just don't leave any more games. LeaveBuster is automated, but it doesn't trigger off of just one game. You won't get punished by the Tribunal for one leave, either.

Just don't keep playing until your connection is fine again and you will be fine.

You dont get banned, or even warning for just one game.
It takes a series of games in a row.

If you are uncertain if your connection is doing good, go play a custom game, leaver doesn't counts on customs.

Alright thanks for the reassurance guys