I wouldnt worry, we all have bad days and the circuit is a busy and demanding place for an experienced pilot nevermind a student.
I myself still get tense when flying but it can only be seen as a good thing because it keeps you on your toes... it's probably good that this happened to you as we all make mistakes and you should learn from them - I imagine we'll all be making a lot more during our flying time so dont worry, its a learning curve!
But, i'll echo whats been said.... it comes with practice and if you can rattle off your Bumpfish and your calls, get your speeds without thinking etc without having to think about it, it will give you more space ahead of the aircraft and then you can sit and enjoy this amazing sport we've got ourselves into.
