That's not heavy at 5'7". I'm about 225 at that height, but definitely not as lean, but my squat and DL have gone up probably 30lb each since plumping up from 210. You're pretty lean and light, so I'm guessing you have a small waist. More size around the middle helps a ton in the squat. Train those abs and obliques heavy and give yourself a built-in belt.
It's all about what your goals are. If you want to make big gains in your lifts, you should add muscle. If staying light is important to you but you still want to be as strong as possible at that weight, you'll have to make sure your technique is flawless to gain every bit of leverage and technique gains that you can, but at some point you will hit a hard wall. It also may be as simple as moving your stance around, or bar placement, or some other fixable issue and you'll jump up over 400. Post a video.