The move from IGCSE to the IB diploma is a real step, and students who expect it handle it far better than students who are surprised by it.
The biggest change is depth. IGCSE rewards covering a lot of ground. The IB asks you to go further into fewer topics and to explain your thinking, not just reach an answer. The habit of writing out reasoning, rather than only the final line, is worth building early.
The second change is independence. Internal assessments and the extended essay are long projects with soft deadlines, which means the students who plan backward from the due date thrive, and the ones who wait for urgency struggle.
If you have a summer before the diploma starts, use a little of it. Read ahead in one HL subject, get comfortable with the command terms, and try one past IA to see the shape of what is coming. A few unhurried hours now save many rushed ones later.
None of this is meant to worry you. The jump is manageable. It is simply easier when you have seen it coming.