For sure, you could stay fairly comfortably on that amount-- just be a bit careful with accommodation prices. Get an Istanbulkart and avoid taxis (unless you need one for whatever reason).
Somewhat on the topic of nightlife: avoid any 'friendly' person on the street who invites you to a bar. That can lead you to going well over your budget ; )

$2,900 for 11 days in Istanbul, excluding your flights and accommodation, is more than enough for a comfortable trip as a solo traveler.
That’s around $260 per day, which is a very healthy budget in Istanbul. You can eat well, use public transportation, take taxis when you don’t feel like using public transport, visit attractions, go out at night and still have money left for shopping and random expenses.
You really don’t need to live cheaply. You can have nice meals, visit restaurants, have drinks, take Bosphorus trips, see the main attractions and enjoy the nightlife without constantly checking your wallet.
Of course, you can spend $260 in one evening if you start going for high-end restaurants, expensive rooftop bars, private tours, luxury shopping, etc. Istanbul can be as expensive as you want it to be.
But for a normal enjoyable trip — good food, sightseeing, nightlife, taxis when needed and some shopping — $2,900 should be more than comfortable for 11 days.
Honestly, I’d be more worried about finding enough time to spend all that money than running out of it. 😄