Hi there, the map should download automatically from the server if you don't have it already in your maps folder, however sometimes if there is an issue with our fastdownloads server - where the map would be downloaded from - when you are trying to connect, it can cause a missing map error.
I just checked our FDL server and it seems fine right now, so I would suggest that you may have a corrupt download of the map in your maps folder.
Go to your TF2 maps folder on your laptop, and if the map you were trying to download is in there, delete it and then try to join the server again. This will force a complete re-download of the map and should hopefully fix your problem.
If you're still having issues post back here and let us know
(or if it works, let us know too lol)