the cat next door

Several weeks ago, my neighbor asked me to watch her cat while she was away. She's lived here most of the time that I have, and we've become friendly; sometimes borrowing a wine bottle opener from the other, things like that. She's my age, and while we are friendly and chat when we see each other, we aren't really friends and don't hang out or anything.

She has a cat and told me that she was going away for a week and could I feed him while she was gone. I told her I didn't mind at all. She said I simply needed to go in once a day, feed and water the cat and scoop the poo from the litter box and put it into a plastic bag that she had in the closet. She gave me a key.

So each day when I got home from work, I'd go next door and play with the cat for a minute or two, and make sure he had water and refill the food. I'd scoop the poo, put it into one of the plastic grocery bags that she left and then put that small bag into a large garbage bag that she left there. She said to just put all the small bags into the large one and then I could take it out at the end of the week. Thursday night when I went in, I couldn't see the cat and he didn't come right out when I came in, so I turned on one of the lamps to find him. He came out a few minutes later. Later that night, I realized that I left the lamp on, but figured I'd turn it out the next day and didn't think too much of it.

She never said exactly which day she was coming home, but I wasn't too concerned. I had her cell number, just in case. I came home Friday night and came into my apartment. I took my shoes off and changed out of work clothes. I sat down to look at my mail, planning to go over in just a few minutes. As I was about to go over, I heard her at her door. I could hear her opening her door and calling out for the cat, so I knew she was home. I didn't want to rush over as soon as she walked in the door, so a little while later, I went over and knocked, but she didn't answer the door. I figured she was tired from the trip and went to bed early.

Now it's a month later and I haven't heard from her at all! I saw her once in the hallway just the other day, and she said "hey, how are you?!" and I replied "great! you?" and that was it. There was no mention of watching the cat, her vacation or anything. She hasn't asked for her key back.

I'm feeling bad about it, like I upset her somehow, though I am unsure as to how! I hope it isn't because of the poo! I had planned to take it out with me and throw it away that last night, but she came home before I could. She had indicated that that is what I should do with it, put it all in a big bag, and she said to make sure to hang it up high in the closet, so that the cat couldn't get at it, which is what I did.

Should I write her a little note and apologize? Should I ignore it all together? What would you do?