Amazon EC2 20 slaves, no master

I launched a cluster with 20 slaves.

Launching instances... Launched 20 slaves in us-west-2a, regid = r-dfce8bd5 ERROR:boto:400 Bad Request ERROR:boto:<?xml version="1.0" encoding="UTF-8"?> <Response><Errors><Error><Code>InstanceLimitExceeded</Code><Message>Your quota allows for 0 more running instance(s). You requested at least 1</Message></Error></Errors><RequestID>5b3a6acf</RequestID></Response>

I understand there is a 20 instance limit, and I gather a master counts as an instance - thus I technically attempted to launch 21 instances. Nevertheless, why would the cluster launch without a master? I ended up with 20 slaves and no master - therefore I couldn't do anything. Even attempting to terminate the clusters via the console proved fruitless and I had to log in to Amazon and terminate them.

To me, this is bizarre. I don't understand why it would launch with just slaves, so I can't access them. Does anyone know if this is normal behaviour and if it is, how do I then create a master in place of a slave?

I've ended up paying for 20 hours worth of EC2 usage for nothing.