You should now be ready to record the event. You have plenty of space on the memory card, so there is no harm in starting the recording 10 minutes early. From experience: It is a common problem to miss the start of the event and people may suddenly start to talk while you were not watching. So just start recording in good time.
If there is somebody introducing the speaker, record this as well (even if you you do not have a mic on them). You can always cut it later. (Imagine the disappointment: Did you catch the introduction by [famous person]? - Ah sorry, the recorder was not running.) Of course without a second mic the sound may not be usable but at least you have it.
As mentioned above: Give enough pre-record time before the activity happens as you want enough pre-roll for the edit and if you do a test recording previously you will also be confident that either the recorder is working fine or you have enough time to sort the problem out!
Remember: What you hear in the headphones is what you hear on the recording so continously check the audio for any outside sound, buzzing or feedback. If you are recording on location and have the ability to start recording again listen out for unwanted sounds that are out of your control, such as trains going past, dogs barking etc.
During the Recording: Whilst recording it is advisable to do some checks to make sure the recording is working properly: