That's the one-biggest complaint I've always had about the 250 Ninja: WAAAAAY undersprung/underdamped in the front - it's like that pair of screendoor-closers Kawasaki puts on the bike isn't suitable for anyone that weights over 85lbs or so........
Fortunately, there's a few ways to fix that in the aftermarket. for about a $75-$90 or so, you can obtain a set of springs (maybe less depending on luck and opportunity). I recommend a straight-rate set, based on yours and the bike's combined weight, and riding style. RaceTech is the brand I've used several times in the past.
One other almost-no-buck method (which is a sorry-arse bandaid patch, IMHO) is to shorten your current springs a few inches and put longer preload-spacers made of PVC pipe in the tubes. But, this can actually LESSEN the suspension travel, so when you do bottom-out it's MUCH harsher.
You really DO need to get something done about this. You should not fear using "all the brake" the front can give you - at the worst case, you might flinch from reflex at a critical time when you NEED everything the bike can give you, and it could cost you considerable pain and hospitalization, or your Life.
I know, you're probably thinking "Idiot! I JUST BOUGHT THE BIKE! - And you want me to modify it already?" Don't think of it as modification - think of it as matching the bike to your abilities, and fixing a serious safety-flaw.
It will definitely increase your enjoyment of the bike.