Although your tattoo shouldnt be ruined by growing, it WILL be ruined by stretch marks. If you are prone to them, they can really mess up nice work.
A good way to keep your tattoo clean and have it heal well is to wash your hands, then wash your tattoo with soap and your hands.....not wash rags or anything like that. Rinse it off, let it air dry for 10 minutes, then put Vitamin A & D ointment on it. Blot it with a clean tissue so that the ointment is just set into the tattoo, not on the surrounding skin. Your tattoo will heal very quickly, and it shouldnt itch at all.