I can't tell you exact steps as I cant replicate the problem - I did what you did, canceled the scan midway and it mounted right back.
First, try rebooting (ultimate problem solver :P).
Second option, Start -> in search box type 'computer management', enter -> Storage -> Disk management and there it should show you your disks, partitions and after selecting the proper one should give you an option to mount the drive (somewhere under right click menu :P)
Third option, Start -> command prompt (with admin rights)
Diskpart (runs disk part console app)
sel disk # (number of the disk with the troubled partition, if only one disk - sel disk 0)
Check if it worked :>
By now it should have worked.
Sorry for not giving you a definite way to solve your problem but as I said, for some reason I cant replicate your problem so I have given some basic ideas that should theoretically work :P