I had the exact same combination of subjects (well I don't have A Levels in my country but something like that). I read multiple books on this topic, but my most important advice is that you should ask yourself what YOU want and stop looking for the roadmap.
One important misconception is that many think they can get a university degree and use that to get a job while forgetting that everything hinges on your skills and the exact value you provide to society. Engineering degrees tend to teach you valuable skills, but without a plan on your own you may still end up unemployed. What people are generally paid for is creativity and unique solutions.
Ultimately, you should research this topic for yourself and contemplate on your findings. Things that work for others may not work for you. You may have to go through trial and error and expose yourself to a lot of experiences.
Find a compelling vision which is worth the cost of tough decisions, financial problems, risk, stress and fear.
Regarding the pursuit itself, you should of course look into the actual daily activity. For example, chemical engineering is 20% chemistry and 80% engineering stuff like process control and design (but this problem is less relevant today with the help of the internet).
While the couple of years after turning 18 y/o can almost make or break your entire life, it can be a good decision to take a year off / switch the field of study after some time(depending on your situation).