What I would do, is go to the far right side, where they let people in that have early ADRs. Tell them you have an ADR for 8:45am.
That might solve your problem. Have your confirmation number with you.
They didn't ask for ours at the gate, but I heard they do sometimes.
If they question it, and they somehow know it isn't until 9am, (if they do have it written down) tell them you were listening to the CM, who told you to be there at 8:45, so that is the time you thought you would say.
Might work?!