Greetings.
There is no risk at all for any STI.
All medical equipment, including ultrasound probes, is either single-use or thoroughly sanitized after each use. The cleaning and disinfecting protocols are very strict; it would be unthinkable for medical professionals to "forget" to follow them. Just imagine all those malpractice suits if they did!
You are definitely overthinking it.
Panicking and anxiety, on the other hand, are real and very harmful (for your baby as well). You may need to seek psychological help.