How to have your own back without beating yourself up?

I’m a freelance personal trainer and I rent space from a gym. As part of that rent I take a couple classes for their members – so I don’t get paid for them but have committed to them.
One of the classes I take is on a Friday morning at 6am. This morning I had forgotten to set my alarm and missed the class. That’s generally something I would never do.
My first reaction is to go to judge myself harshly and feel a lot of shame but I’m trying to learn a new way of dealing with these kinds of situations. Generally in life I want to learn to have my own back no matter what.
But it’s almost as if I don’t even know what a voice would sound like if it wasn’t either judging harshly or just being apathetic – my other option for when i get really tired of judging myself.
I mean it’s not the standard I would like for myself – I made a commitment, let people down etc.
I suppose I’m trying to find the line between feeling the discomfort of that without shaming and criticizing myself.