I AM SCARED

So today when i was at school me and my friend were hiding in the bathroom and i jokingly said oh im going to go finger my self and so i did but i did go like upa nd down i kind of just stuck my finger up (it was clean) and i look at my finger and it had blood on it and bleed a little bit onto a sheet of tolet paper and there were a few dots when i was anout to change the tolet paper but idk but i got really mad cuz i wad laying down on the ground with my friends and a teacher walks by and it was my math teacher and he asked if it was me an di said yes and then HE asked if somethi g was wrong and my friend just screams yeah its her time of the month and she isnt very happy about it but what should i do i mean i have a older sister but she has tampons and i dont want to use tanpons at school cuz of the shock syndrome thing but could it be like could it be just my body getting ready to start my period or i just had a minu one and not realise it.... HELP ME!!!!!!!!!