You can use the lounge lockers, but you need to be careful to not make it obvious that you're putting a bag into the lockers and intending to leave the airport.

Probably worth reviewing this previous thread of mine as it has the entire process laid out for you around post 18 if I remember correctly. Whilst the thread is several years old I think it's all relevant still, the only significant update is that Doha metro is now an option for travel to/from the city if not in the middle of the night.

QR free transit visa - DIY Doha night tour?