African Mask/Alocasia care HELP!

A clue may be in your statement that you water it once a week.
It's possible that you are over watering it, as they don't like being watered too much.
So if try to "up" the humidity, as Nan suggested and not water it as much.
With regard to your embarrassment at your family knowing their present is not faring too well.
I have been known to nip to a local garden centre or B &Q and replace a plant bought for me.

I would think, the larger the tray, the better, depending on where you are able to keep it. Then the rising humidity will hopefully envelop the whole plant.

Hello NanTheWiser,

Thank you for the advice. I have a contained oil heater in my bedroom, but I like it very warm, but may have to turn it down a bit if my plants don't care for it! (My husband would like that, he claims he is roasting in there)

Your recommendation of a pebble tray, how much wider should it be to the pot base, a small saucer underneath the pot or a larger breakfast style tray?

There is only one leaf left - I trimmed the others off!

I would be very embarrassed if I killed it as my family all think I have green fingers in all things plant related

They are not the easiest plants Dilly coming from tropical habitats, which means they require warm and humid conditions. Maybe misting every day is not quite enough, especially in a warm room where the air will be quite dry - you could stand it on a tray of pebbles kept permanently damp, which would create a humid microclimate. Are your oil heaters the self contained radiator type? I ask that, as an open oil heater will give off harmful fumes, which might affect such a tender plant.
Good luck with it!