We can't answer that only you can.
Take a pregnancy test if you think you are pregnant - though having a period usually means you are not - it is not 100% reliable .
Just because a period is a few days late is nothing at all to worry about - it happens to everyone - not any woman on this planet has an exact cycle throughout their lives.
some are short months sometimes periods are late for weeks at a time, some are light some are super heavy - some cramp more than others. It does not necessarily mean anything is wrong - it could be the result of being ill, or stressed, or a shock like a bereavement, or a change in environment. Could be due to medication or just one of those weird events that there is no explanation for.
But if you do know you have had unprotected sex and are not deliberately trying to conceive then do take a test. So easy to do that these days and to sort it out if you do not want to be pregnant and by accident find out that you are.
And if you are not wanting to get pregnant - then use precautions next time so you don't have the worry and more importantly don't risk STDs.
As this is your 1st post - were you worried that you might have endometriosis on account of this one slightly late period ? Or are you showing signs of other symptoms?
If what you have written in the sum total of your concerns and you are not thinking you have endo or are not diagnosed with endo - then I can catagorically say what you have written down does not indicate endo. You sound like you have been exceptionally lucky in the past if this is your 1st blip with a period. Perhaps you are very young and unfamiliar with the disease or indeed with the menstual cycle and all its possible quirks.
What you have described gives me no cause for any concerns at all other than the fact you think you might be pregnant which means you have had unprotected sex and were not expecting to be pregnant and have not first checked it out before posting here. Please visit a chemist or supermarket and buy a kit to put your mind at ease - or visit your GP as a non -urgent appointment to get checked. All you need to do if proved a sample of pee.