No you're not being unreasonable:
was told it would take a few days
^^ that's the crux of the biscuit right there, and if that's what they said, hold them to it.
It's not like they could be surprised that they are busy at this time of year. Any time estimate should have taken that into account. Also I think that if you have special circumstances and told them that you needed it by a certain date/time, they should have made a plan and prioritised - that's all part of running a repair service IMO.
