Don't worry too much about it mate ... the harshness of the IRT test is a joke, when 13 out of 15 airline cadets can botch it (bearing in mind they have theoretically all been hand picked as being of above average ability and low training risks) then something really needs to be done about it.
I was fortunate enough to get it first time but on reflection I was amazed, there's no doubt the examiner 'could' have failed me on at least two sections if he had been really in an arsey mood. The standards they set in the manual are simply not possible for normal mortals, it's rigged so they can always get you for something if they want to.
I'd go for the series 1 - attempt 2 option myself, you've not really got anything to lose by trying it and possibly a lot to gain in terms of compulsory dual hours. If you were only a narrow fail the first time and you get the same examiner, they'll quite often take a bit of pity on you in my experience.