Is a person sinful if they have to make up a few prayers, and they make up one prayer a day, but do not make up prayers on working days?

If prayers are missed due to an excuse such as sleep or forgetfulness, the Shafi'is are of the view that immediate making up (qada') is not obligatory, although it is more prudent to make them up immediately to avoid scholarly disagreement. However, if prayers are intentionally abandoned, the majority of scholars—including the Shafi'is according to the sounder opinion—hold that making them up immediately is obligatory. In summary, it is necessary to make up prayers immediately in every case, and this is especially emphasized if the prayers were missed intentionally.