A lot of DP2 students arrive at application season without a clear sense of what they want to study. That is more normal than the system lets on. The problem is not that you are undecided. The problem is that the systems around you pretend you should be decided.
The decision you are actually making
At this stage, you are not choosing a career. You are choosing a field of study for the next three to four years. Most people who graduate in one field do not work in it five years later. That is fine. What you are really deciding is which type of thinking you want to practise for a while.
Three questions that usually cut through
Which of your IB subjects did you actually enjoy the thinking in? Not the grades. The thinking. If you kept reading around a subject even when you weren't studying for the test, that is a signal. If you found yourself wanting the course to end, that is also a signal.
What kind of environment do you work well in? Large lectures with fast-paced content. Small seminars with slow, discussion-heavy reading. Lab benches. Studio desks. These are different lives. Pick the one you have evidence you thrive in.
What trade-offs do you actually want to make? Employability vs flexibility. Specialisation vs breadth. Prestige vs fit. There are no right answers, but the decisions cascade and you will live with them.
A useful framework
If you genuinely cannot decide, default to the broader option. A broader degree (economics, philosophy, a liberal arts college) gives you time. A narrower degree (law, medicine, a specific engineering track) locks you in earlier. If you are uncertain, the cost of locking in early is higher than the cost of specialising late.
The thing that no one tells you
The university you attend will matter less to your eventual life than how you spend the four years there. A student who uses Oxbridge passively is outpaced by a student who uses a tier-two university actively. The application decision is important. It is also not the last important decision you will make.