When should I take a pregnancy test😬😬

How long after having sex (30th December) should I wait before taking a test to ensure that it’s as accurate and effective as possible. I’m quite impatient and really want to take it now but I really don’t wanna get a false negative/ positive. The reason I’m not going off a missed period is because I’m not sure when I’m meant to be due. Really hoping for a bfn, we used protection he didn’t finish anywhere near me and I took a Ella one but I’m a massive over thinker plus I’m only 16 so lol help xx