After the opening kill, side shots of the getaway car show it parked rather tightly between cars at the curb. But a cut to view through the windshield shows a considerable gap before the car that had been just in front before the driver pulls out.
At the very end, you see her open her mouth to reveal a 14th bullet, then a flashback to the Doctor putting it in her mouth with his. However, when she first wakes up from her "death" she gasps for air and her mouth is wide open. If there was a bullet in her mouth she would have choked on it. Of course, she could have taken one from the clip of the first guy she killed, but you don't see that, and there would be no reason for the flashback.
During the gun battles at the end of the movie, the billionaire is counting the bullets fired. Since he has no clue what make and model gun Miyumi is using, he would have no idea how many rounds it holds.