What's the possible way to stop being late?

My school ends at 3:00pm ..and i leave the school straight away. I walk with my friends all the time. Somehow i always comehome at 3:30 all the time because i'm just talking to my friends for like 15-20 minutes. (i don't have any cles with them so i don't normally get to talk with them). I never get in trouble. At times I do. I just can't seem to follow the timings very well, when i have a time to be home and then i come home late. I'm trying to stop it but don't know how! I need some advice. It happened today actually. It was the embly and i had to be ome by 1:30. I really wanted to take a walk by bayfront with my two friends, and we vowed to be back by 1:00pm. then we came i came back by 2:00. and i got yelled at. Should I tell the truth or an excuse?? PLEASE HELP!