knitting vertical stripes

have started a scarf with 2 stictches of colour cherryred, then a block of 16 stiches in colour lilac, then ending with 2 stiches of cherryred colour. 
however the beg and end stiches are working up separate from the block, its like i'm knitting 3 individual items on 1 needle. i'm surely doing something not right. can anyone please explain? thanks