I'm confused on when I conceived and they told me I conceived on the jan 3rd but my due date is sept 17 I'm real confused

There is no way anyone can know exactly what day they conceived unless you only had sex once during a several week period. They are only estimates, just like your due date.

It will be some time between your last period and when you missed your next period.

Estimated conception dates are really plus or minus a couple weeks, Really does not matter what the date is, unless of course there are more than one sex partner

What part of it confuses you?

They can only guess your conception and due date. Once you have an ultrasound, it will become more accurate. Due dates are initially calculated based on your last menstrual period which means at the time you are late for your period, the pregnancy is counted as 4 weeks along even though you probably conceived 2 weeks before that during the fertile part of your cycle. (This varies with each woman which is why the due date and conception date is only an educated guess)