You should ASAP. Always.
You do not tell if you were required to be at that meeting, but I assume so.
You already attracted attention by not showing up.
Whether it will "make me worse off for bringing attention to it" depends on several factors (I will even include "make you better off", and I assume that the apology is real):
You apologize early
People will recognize that you realized missing the appointment has consequences. If these were small they will wave it off, if they were big they will probably emphasize the consequences again. You may have to repair one of these consequences.
They will know you for 'the guy that missed the meeting and has the guts to acknowledge that'. Assuming that you do not repeat you will leave a slightly negative to a positive impression.
You apologize late
This will raise eyebrows - they will wonder why you bring it up this late.
Also, the consequences of you missing the meeting will not have changed.
If they were big somebody else had to clean up for you. In that case, you definitely should still apologize, and the mess to clean up will have grown.
If they were small, people, with time, may forget that you missed the meeting, but that won't happen fast.
You will not leave a positive impression in both cases.
For what a 'real apology' is (not) you should look at this video: How to Apologize like a Fartbag