Without trying to seem too cynical, the recruiting process is about meeting predetermined sets of criteria and little else - it can rightly be called a "numbers game" although this is perhaps painting too bleak a picture.
If OASC don't want you as pilot at this time because of your scores, then that is the state of affairs and unfortunate luck. If there is a glimmer of hope of a "back seat" job then by all means go for it using the normal arguments about wanting to be a combat flier etc. If this does not work then accept wholeheartedly the FC slot. A word of warning - don't think (as some may say) that you can rebranch during IOT or during ab-initio training. You can't! There was a time when, if there was slack in the system, you could attempt this, however if you VW (voluntarily withdraw) from training hoping for a rebranch in the current climate (or worse still, fail "tactically") then you will be back into civvie life! The RAF is too small nowadays!
Don't be too dishearted about the prospect of 6 years as a FC. I believe the chop rate is not all that high and that this rumour dates back to the days when failing Weapons aptitude and being streamed Surveillance was seen as being chopped. I don't believe anyone is likely to be offered a PC on commissioning so you will have to work for one after a few annual appraisals along with everyone else. You will gain a far better tactical appreciation of the modern battlespace as an FC than in admin, supply or ops support, and these areas (I believe) are likely to see compulsory redundancies. And, once you have your feet under the desk as an FC and are looking at a PC then you could try again at pilot/nav, once the folly of the current cutbacks are recognised and the redundancy pain has bitten. In all likelihood you will be very competitive at the appropriate time ie. once the cutbacks have been recognised as the insanity there are and the RAF tries to redress the shortfall of aviators.