I have one plant that is far behind all the others...

It happens when you plant your seeds some will come out stronger then other thats normal . From I can see in your pictures theres nothing wrong with your plants they are happy and healthy , the only thing i might suggest is using abit of CalMg this will get rid of your red stems . You can do it by either mix it up with water in a spray bottle as a foliar spray or you can just add it to your plants feedings . Either way your plant looks completely normal . Some plants have different pheno types because its a multi genetic plant but the differences wont be really big as most of the genetics out there are pretty stable . All in all I'd say keep up the good work and get ready for a kick ass harvest ! I hope this information helps you ! -Happy Growing!