I am almost 30 year old and female i recently found out my gfr is 40% how worried should i be?

Concern: That is something of concern. You are young so there must be a reason for the low gfr. You should see your doctor and/or a nephrologist to determine the cause and if it's reversible or manageable. Causes could be diabetes, hypertension, an infection, stone, or one of many kidney-specific diseases.

Agree with Dr. B: It is a serious issue and you should consult a kidney doctor, nephrologist, at your earliest.