I went to put the cap back on and noticed that the plastic collar below the rotor is extremely loose.

I don't think it was before.

It's the plastic part directly under the rotor that says Start and finish on it.

What do I need to do to fix it?

as long as that plastic cover (with start / finish on it) is seated down onto the distributor, then the cap will hold it down. It just sits there on its own with the dist cap off, and is located by a slot

Yeah it's seated on it, I'm just wondering how to align it to where it was before?

Where is the slot? I've turned the plastic cover around and it's not locking in to any slot.