Chemically straightened hair?

I had my hair chemically straightened and about to get it done again(i get it chemically straightened about every for to six months) and i now maintain my hair using a flat iron and straightening shampoo and i use hair serums b4 using my flat iron. My hair is currently one inch above my shoulders and it is layered ,my hair is straight when i use my flat iron but the ends of my hair curls up and i hve healthy hair. Any suggestions on wht to do to keep the end straight like the rest of my hair. Sorry its so long but thanks for taking ur time to read it