The deploy image task also has partitioning built into it, I suspect what's happening here is that you are creating the partition using the task above and then the deploy image task's partition settings are deleting partition and re-creating a new one using 100% of the disc.
What you need to do is go into the advanced settings of your Deploy Image task, the first tab there is for partitions, set your 60GB here.
It's my understanding the create partition task is used to create partitions on the disc that will not have an image deployed to them, for example, we deploy a server 2008R2 image to a fixed size partition and then use the create partition task to create a data partition, NTDS partition and an apps partition.