I had sex for the first time when I was 14, So I know what is running through your head at the moment. Now 13 is very young and have you thought of all the consiquences of having sex at that age?. Just remember, boys do tend to talk and it may not remain a secret between you. Also the boy you have sex with could break up with you and move on, he may not stick around.
Another helpful tip to remember is that your first time is nether romantic or un-stressful.PLEASE USE PROTECTION. Condoms must be used reguardless of your age or wether your a virgin or not. Now It is compleatly your choice to do it, don't let anyone on here tell you what to do, just PLEASE explore your options.
If it hurts you can maybe suggest that you slow down and get into some foreplay, say somthing like " I want you to go really slow and tease me" therefore he thinks going slow is a turn on. without having to say its hurting you.
You can also change the positon so your on top, if your on top your in control of the pace the deepness and the speed.
Invest in some Lubricant, Ansell is VERY good, ITs clear and odourless so you won't even realise your using it. It makes it easier to slide in and makes it smoother so if you go dry during it, it won't Rub, hurt and cause irritation.
I hope those tips are helpful.
All i ask is before you two have sex think very carefully wether or not you REALLY want to do this, If he REALLY loves you then he shouldn't care wether or not you are having sex. AND PLEASE USE A CONDOM!!!!!!!.
LET ME KNOW HOW IT GOES!! ADD ME!!