Should i go for itWatch
Have you tried talking to the head of the IT department, or your future teacher and outlining the circumstances to them? I'm sure they would be willing to make an exception if you can show them that you achieved the highest possible grade. As for retaking a year, I'm not sure that it's completely worth it. Instead you could either just apply for the resits in November or alternatively ask your teachers to facilitate a internally assessed exam. However, as I did higher tier I wouldn't be able to accurately say, but I know of people who went from foundation to higher with a very small learning curve (someone I know went from a 5 in foundation to a 7 in higher!), however I also know people who immensely struggled with adapting to higher tier.
So I guess it's down to whether you believe in your ability, and by the looks of it, you're more than capable of smashing higher tier!
Anyway, my advice would be to first consult your future teacher/HoD, and then go through potential options with them.
I hope it all works out well!