I am 11 weeks pregnant and accidentally ate a few bites of an undercooked hamburger. Should I be worried about toxoplasmosis?

Would worry. More about e. Coli. Only if the hamburger came from a toxoplasmosis infected cow which is less likely than e. Coli but wouldn't be overly anxious. See your doctor immediately if you develop any gastrointestinal symptoms over the next few days.