Thanks - you should see the status of your instances in the Spot Requests section of the EC2 console within your AWS account.
Spot requests are not always instantly fulfilled - so nodes may join much later than any initially obtained instances. It is worth checking the Spot Requests page to see the status of each instance.
Navigating to the AutoScaling Groups section will also detail how many instances are currently running within your AutoScaling Group. Should you wish for more or less instances, you can click the Edit button on your AutoScaling compute group and change the number in the
Desired Capacity field.
Hope that helps -