First time here so feel free to LYAO at me.
I planted seeds in a tray (stocks) and the bloke at the garden centre said to put the tray in a polythene bag. I didn't have a clear one so improvised with cling film. That was 10 days ago. I left it on my kit hen window sill. There now appears to be white fluff, I think it's mould. What do I do? Have I buggered this up completely?