I have to say my first couple of attempts were not great! I now add 1-2 tbsp of water to the egg yolk mixture to make the consistency looser, then I sieve in the flour (or flour/cocoa powder mix), mix that in fully before whisking in the egg whites about a quarter of the egg white mixture at a time and then giving it all a really good whisk up before it goes in the tin. I knew I'd got it right because it had risen loads in the first five minutes and that had never happened before!
Give it another go little hobbit, double check you had the right measurements and as Stacey said check you are using the right flour. It's worth it in the end!