Recently I have found a knot in my breast that is visible (can see lump under skin). Should I worry. 24yrs old?

Seek medical eval. While the likelihood of having breast cancer at 24 is very, very low, any new lump in your breast requires medical evaluation. Accordingly, i recommend that you make an appointment to see your gynecologist or primary medical doctor. Chances are this is a benign tumor called a fibroadenoma, or "lumpy bumpy" breast tissue, aka "fibrocystic changes".
Keep an eye. Observe and see if the knot disappears over the next few months. Often, young women have cyclic changes to their breasts with their periods. If the knot persists, or if you feel that the knot is getting bigger, see a doctor for further follow up. Rarely, thrombophlebitis of the breast (mondor's disease) can manifest as a knot.