Help, how to improve?

Hi, i’m a current year 12 student taking Maths, Physics and Chemistry, alongside an EPQ on Green Chemistry.
My aspiration is to hopefully study Chemical engineering at Cambridge.

My GCSE grades are 888887776 and my predicted A-level grades are AAA, I’m trying to boost them up to A*s by time I start year13.
I’ve read that a lot of people who intend to apply to oxbridge are doing many super curricular activities, though i have no idea what i should be doing.
The only ‘extra things’ i’ve done are:
- Bronze, Silver and Gold (still running) DofE. Though I heard Oxbridge doesn’t really look at these.
- Extra reading for physics
- Online course on chemical engineering
- Hospital pharmacy work experience

I've also applied to their summer school via Sutton trust, however I doubt i'll get in.

Is there anything extra i can do? Any courses, extra readings or challenges?
Or should i just forget about applying to oxbridge all together as honestly my GCSE grades are below expectations.

Please let me know. Thanks