Okay. There are a few things you can sort, a few you need support with (and document all of this).
Behaviour.
Are your teachers following the system to the letter. And I mean setting detentions, recording everything, parental contact - the whole shebang, If yes, brilliant - get pastoral and the head of behaviour involved to deal with disruptive kids. If not, you need to manage that and hold your team accountable.
What is your departmental support system? Do you have removal rooms, do you take on some of the kids to give your teachers (and their classes) a break? Do you deal with students and their parents where your team needs support? All of that falls on you I'm afraid.
Curriculum.
Bit late in the day for massive overhaul. Most core subjects are staring revision. You need a decent basis covering all aspects of the spec. Great if you're delivering it already. Divvy it up, have everyone contribute to their areas of strength. Their responsibility to make key resources and find appropriate exam practice. Produce a bank of common, overlapping questions and get the kids to do extended practice once every 3-4 lessons. Have a plan in place for next year. Backup resources privately so arseholes with a grudge can't delete their stuff.
Other results things.
Parental contact to all underachievers with a breakdown of areas of concern. Leaflets with QR codes for resources for all learners. Speak to Heads of Year, form tutors, pastoral leads and Y11 mentors (such as your Lead Pracs). A bank of full resources for persistent absentees on whatever platform you use. After-school revision and holiday revision if you must. Robust cover lessons for absent staff - use oak academy if you must. Buy in revision guides (with parental contributions or nag someone in SLT with budget, for example PP).
Yes, all of that is on you. No, the TLR isn't worth it.
Document everything from the above list you've done. Document every lesson you lose to core subjects or workshops in the run up to exams. You prove you've done your bit, SLT will have to accept you cannot work miracles.