Mel is absolutely correct.
Recently I replaced the weather strip on my tip-up crash bar/canopy interface, but used stripping that was a hair too thick. I thought I had pulled the canopy down fully before locking the side handle, but the left side hook disengaged just after lift-off. The closed top handle kept the canopy from opening.
Another time, I missed closing both latches before takeoff (human factors: Distraction and Checklist Discipline). On liftoff, the canopy opened about 2 inches, and I could not pull it down due to internal/external air pressures. I throttled back a bit and climbed straight ahead several hundred feet, then bunted the nose down slightly. This put enough air pressure directly on the front and front-top face of the windscreen to push the canopy down. I then could latch the side and top latches. My Before Takeoff flows changed from that point on.