Look at the weekend as it is
A weekend may appear empty in a work calendar while already containing shopping, family plans, a long drive and household jobs. Write those commitments down before placing missed workouts into the remaining gaps.
If you normally train at weekends, protect the session you can realistically attend. Adding several replacements around it can turn the original plan into a much heavier weekend. A missed weekday session does not become more suitable simply because Saturday has no meeting invitations.
Check opening times and travel arrangements too. The gym may run shorter hours, and a journey that is quick on weekdays can be different during local events or transport work.
Choose what matters this time
Perhaps one appointment fits comfortably and a second would require cutting into sleep or cancelling something important. That is information about this weekend, not evidence that the entire routine has failed.
Keep a clear distinction between a planned training day and an optional outing. A walk with friends need not be extended into a demanding session to compensate for Friday. Likewise, an activity you enjoy does not have to be entered into a workout tracker to count as part of your weekend.
If missed sessions repeatedly collect at the end of the week, change the weekday arrangement. Moving the same problem to Saturday over and over is usually a sign that the original schedule needs attention.
A booked class may also have a cancellation policy. Check it early rather than waiting until the last moment to decide. Releasing a place appropriately is considerate to other users and removes one source of unnecessary pressure from a weekend that already has competing commitments.
Prepare the next starting point
Before the weekend finishes, check the next gym appointment and the session you intend to follow. Set out what you need and leave the previous week's unfinished entries in the previous week.
A short note about what disrupted the plan can help with the next review. Beyond that, there is little value in calculating how much you owe. The next useful action is an appropriate, workable session, not a repayment schedule built around workouts that did not happen.