dev/sda is the same as HD1 or hard drive #1. The problem may have been with the burned disk not being read for a second while booted live from that.
Remember moving any good sized partition means no interruptions while in progress. Once you set the amount of drive space proceeding C to 0 and click on apply GParted then starts moving the primary by copying bits at a time from one place to the other to see it reassembled there.
Have a lens cleaning disk onhand? Once the beginning of the partition is at the 0 bytes spot the next step is simply to click resize and grab the end of the indicator tab like clamps and drag that end to the back of the drive to then click apply for that.
Even if you decided to remove the hidden recovery partition you would still have to move the C primary to the front unless planning a totally fresh start on a new primary simply to save on time. Partitioning time that is not installing everything over from scratch.
"what did I do?"