First of all take a deep breath and relax......
The application isnt much more than a way to gather your details and determine your suitability to apply for ATC or not. As long as you meet the minimum requirements as stated on NATS website you have nothing to worry about.
The way to HR's heart is to do well enough in each of the stages of the application process-These include testing and interviews. If you succeed at each stage you will be passed along to the next.
Make sure you have spelled your name correctly and submit your application and stop worrying mate.
best of luck to you!