While obviously Oxbridge and similar (Imperial, LSE, UCL, etc.) want to see applicants that have undertaken three A-levels over two years, other universities may be more flexible in considering you if you sit 3 A-levels over 3 years (i.e. sit two A-level exams next year, then one the year after). Bear in mind no matter what, your learning experience has been disrupted to some extent by the coronavirus situation, so I imagine many universities will be expecting to give the benefit of the doubt for the next application cycle (at least) to applicants who were studying during this time.