Stork - sorry, I missed your post earlier.
On the plus side it sounds as though your clinic have been absolutely honest with you, which I don't think all clinics are. Just because the embryo isn't 'optimum' it doesn't mean it isn't a good one. They wouldn't do the transfer if there wasn't a good chance of it working.
(IUI ladies put a blindfold on for my next sentence. I'm purely in the business of making Stork feeling better here...)
Compare your 49% chance to the 18% average chance with IUI!
Now your job is to look after yourself, keep yourself happy and well-distracted so that you're not dwelling on the time that has to pass before you can test.
This thread is just bursting with TWWs at the minute. Its a wonder it doesn't explode with the suspense!