How should I respond to this email?

I had an interview for a job last Monday. I received a form in my email for a drug screening on Friday at 1:00pm but didn’t see it until like 7:00pm. I was just gonna go to the clinic to do my drug screen on Saturday but I found out they don’t do it on the weekend so im going to do it today. I just got an email from the employer checking in to see if I got the form for the background screening. Well I have but I just haven’t got around to it yet for the reason stated above. I really want this job and I dont want them to think I’m not interested. What do I say? So it really is my fault because I didn’t check my email until it was too late.