Can donating 350ml blood twice in a month leads to anaemia?

Probably ok ..: ... if just ONE month. But THE VERY MINIMUM recommended interval here is 8 weeks and most centers recommend every 16 weeks/4 months for menstruating females such as yourself. Remember you are also losing blood monthly in your period. Check with your local donating agency for their guidelines.

No: Look for some other cause. This can unmask iron deficiency. If your hemoglobin is just slightly below reference range, and you donated very recently, I would not be concerned.