So I need to get an expander tomorrow... I had spacers in, but at my second appointment, I had gotten my moulds done for it and they put the teeth spacers back in, my spacers fell out because the gap was already big, my mum and I couldn't get my spacer back in, and I think the gap has closed up a bit, will they still be able to put the expander in? I'm scared the gap closed too much and it won't fit! Thanks in advanced :)

I am sure this is something the dentist has run into before. I don't think you need to worry about fit.