My view is to go through the specification. Your school will be teaching the same exam board for both three separate (triple) and combined science. If you go through the specifications for GCSE Biology/Chemistry/Physics, often the content that's not in combined will be pointed out, e.g. in the AQA spec for each science, the triple extra stuff is shown as "biology/chemistry/physics only" for each spec point, and most textbooks point this out too. Take a look at the biology/chemistry/physics only spec content and decide whether you'd find learning that additional stuff too hard for you.
I think you should give the triple mocks a go if you can, your Y10 mock result appears to show you are at an appropriate level. Ask your teacher if they can assess you on that content too e.g. taking a triple mock. There's no harm in trying. Just give yourself enough time to revise, and if you pass the triple mocks with a grade around your predicted grade, then your teacher will realize and will probably upgrade you to triple.