when i go to stroke it i flinches and jumps ..
Well, if your hamster is a dwarf or a robo hamster I think this is just normal for them to be this jumpy. If your hamster is a teddy bear hammy (The big ones) you should just feed your hamster some treats and while he's eating slowly stroke it's back. Of course, some hamsters are just jumpy by nature and it really depends on the hamster's personality to see if it'll trust you. It takes time for a hamster to trust you and maybe with a lot of handling, feeding, and time your hamster will learn that you're not evil.
Best Of Luck ~
How long have you had the hamster? It will take time and here is a tip, try and give him a favorite snack so when you hold your hamester he is getting a double treat, you holding and caring love , and the treat. I think that will work.lol
you might be approaching it too fast, move your arm calmly and slowly the whole time to ensure you dont scare it, but it might just need a bit more taming to stay social
Make it do a trust fall.