Hey, no-one but NO-ONE is infallible. Every single one of us is going to make mistakes from time to time so if it was something you overlooked, well all that shows is that you're human. And let's face it this seriously isn't a major mistake, despite how it may feel.
So deep breath whenever you're feeling like this AND is it really your fault? Check with your bank to see if the money has been taken out, if not who knows maybe the cheque got lost in the post.
Anyway, regardless of what actually happened, maybe put in place a system to help you to avoid this uncertainty if it happens again e.g. write in your diary or on a calender (somewhere obvious) when cheques need to be made/sent and tick/sign off/date when you've done it.
Hey, sometimes it's actually good when we make mistakes IF it was down to you. That way we can plan and organize ourselves better to avoid even bigger mistakes.
So smile Nothing wrong with you!! Congrats on being human just like the rest of us

Take care and DON'T be so hard on yourself in the future!!
Alison