Avhaben: Cherrybim is completely correct. It does not even have to be a long shower. And you do not have to be entirely immersed at once. You just have to make sure that over the course of the shower that 9 Kabim touch you (which will definitely happen) and that water hits everywhere. This is a Gemara in Brachos that Daf Yomi will get to in less than a week.
(If I recall correctly, some Achronim are Machmir that 9 Kabim was only for a Zaken or Choleh but that wasn’t what the majority of Rishonim held the Gemara’s Maskana was.)