As PowerBuilder said, focus on your 30m sprint. You'll find most sprinters seldom sprint 100m for their training, it's about improving their reaction time and their acceleration - by the 30m mark they've usually hit top speed and hold that for the remaining 70m.
Doing sprints with added resistance (sand sprints, hill sprints, parachute/weighted sprints) will all help with improving your acceleration. Keep your sprint distance to 30m - that's a good gain on any rugby pitch anyway.
A good squat exercise to try is this; get yourself in to a squat rack and set the safety bars at a height that allows you to get under the oly bar in a fully squatted position. Load the bar up and squat up explosively, rack the bar on the safety pins. There are no negatives, you're focusing on the explosive, positive movement. This will build explosive strength and limit your size gains.
Don't forget your benching and rowing, rowing more-so, you want explosive strength in your upper body - ability to drive your arms back hard whilst sprinting. When doing your sprints be mindful of pumping your arms.