Im trying to install a Seymour Duncan jb humbucker into my currently sss strat, can somebody link me a pickguard that will fit the pickup as the one I ordered is too big, thanks
Too big how, and what did you order? Any HSS strat should have standard humbucker dimensions, unless you got a really cheap ebay one from a seller who doesn't know what they're doing.

You also need to specify the type of strat pickguard you have, there isn't just one. Most Fender and Fender family models use a standard size that differs only in the number and location of screws affixing the guard to the guitar.
any pickguard should fit it i'm not sure why it would be too big as everyone just copies fender dimensions for strat knock offs and all.

one of my favorite suppliers of pickguards is below , just make sure that the routing is right
20+ colors and very affordable. I've put these on many strat copies up to fender mim to deluxe

http://axetremecreations.com/ - very custom
qparts.com for more customized parts