Extra costs for my first Gurgaon flat are shocking

Sector 26A — my broker keeps pushing properties here, saying it's the next big thing. I'm looking at an Advance India Projects Limited project there, around ₹1.2 Cr for a 3BHK. But honestly, the 'extra' costs are scaring me. Stamp duty, registration, then interiors... I had no idea it adds up so much. My parents keep saying factor in at least 20% more, but is that enough? What did you guys budget beyond the property price? Is there anything else I'm missing that nobody tells first-time buyers until it's too late? Ab samajh nahi aa raha if my budget is actually realistic.