Wrong flight, cost advice !

Hi everyone ! I was hoping to get some POVs and advice regarding a dumb mistake I made. I booked my boss a travel which they do on a regular basis. Up until recently the travel times were always somewhat different, depending on the need. We discussed after their last trip that I’d book specific times for the next one. I was tired today and double checked the right time to fly based on the wrong previous flight, not the one we discussed. I know this can happen but i’ve been on icy terrain lately and I’m really pissed off at myself for making that mistake - i knew I was tired and should have just waited until next day. They are asking me the cost to change which is pretty minimal but I feel really terrible about this and almost want to pay out of pocket. I know it’s dumb but I’m struggling to think rationally about this after having been on thin ice (due to my own issues). Thank you for any advice on how to deal with both myself and the right reply to them! Much love