bleeding is usually scanty and lasts for 1-2 days. In a women who is having regular 28 days cycle it should occur on 21-24 days. In your case you had spotting on your 21 st day (25th march) so it could be implantation bleeding. Its better to wait for few days and confirm it by urine pregnancy
test. If you r anxious you can get beta-HCG blood test
done now itself to confirm. Take care.