Alamak, I understand la worry-worry macam ni, especially first baby! Honestly, bladder size varies from baby to baby and even the measurements at scan boleh jadi slightly off depending on angle and position, so don't panic too much yet, a few of us went through different measurements and baby turned out completely fine. Best thing is to discuss this properly with your doctor at the next checkup so they can monitor and explain lah, depending on your whole scan results and situation. For now try not to stress yourself out, stress also not good for baby, tapi do mention it to your gynae yah!