Thank you for your query at DoctorSpring.com
I understand your concern.
Yes an isolated shot of 2000 mcg of methylcobalamin won't cause any damage. Only when it is taken for a period of time, toxicity can occur.
Secondly, if the liquid was indeed cloudy, you would have manifested symptoms right away.
Since 24 hours has already passed, you really do not need to worry about any emboli.
Feel free to discuss further,