Overtime on a Saturday Morning

I'm currently rendering an overtime on a rest day. Half-day lang naman. Though I'm not sure if it would be appropriate for me to ask for a pay for this because during the days I am not doing what I'm supposed to do resulting into this piled up job I currently have hence the OT request, I am getting paid in full. I even get paid in full during my absences when I got sick for a whole week but I think that's just right. I was just thinking I'd be unfair to my boss if I still ask for a pay for this OT request, though he's the one who really requested it. I'm handling the company finances and it's now in really bad shape and we already lost track. So I need to catch up on this right away or else, I'd be having the same issue I had this month in processing our salaries. Our salaries have been delayed because I am not doing my job properly. Shame on me.