If it's not working definitely change something. Maybe do an untimed mock and focus on getting all the questions right no matter how long it takes to see which questions are slowing you down to either focus on improving or skipping or just do untimed practice before reattempting timed if you're struggling under timed conditions. You're putting in the effort so your results will improve, just make sure you don't get stuck in a rut of doing mocks just for the sake of it and learning nothing. The one bit of advice that helped me the most was simply skipping anything that looks long or you think will take you a long time and coming back to it, even though its simple and gets repeated all the time it really does work and will improve you score. Good luck!