I've been to India, and I'm quite sure nobody I met except maybe the hotels serving tourists, was paying taxes. Shops, restaurants, businesses all only accepted cash. And they also never give a receipt. So yeah, 3% sounds about right.
I live in South Africa. It's a similar situation here. The problem is that most people are so poor, they legally don't have to pay income tax. (because they are unemployed or have a really shitty income)