dude, how can you not firm it?? if u do firm it at least there is a probability you will get in. your argument so far is "I don't think my chances are high so ill reduce it to 0" do u see the issue?. if i were in ur place i wouldn't even consider dooming my self. wasting a slot is bad but the thought of getting the grades but not getting the place because i didn't firm it is even scarier. besides unis will be flexible this year they may say u can differ ur offer to next year if you sit the autumn resist or they might just accept u anyway even if you don't meet the grades because loads of ppl decided to take a gap year and they have vacant spaces.