Hello Aditi. Bread can turn dense for a few key reasons related to your technique.
First, under-kneading fails to develop sufficient gluten structure to trap gas, while over-kneading can exhaust the dough. Second, under-proofing means the yeast hasn't produced enough carbon dioxide, whereas over-proofing causes the gas to escape. Finally, incorrect moisture ratios—like using too little water or too much heavy flour—will heavily restrict crumb expansion.