Redownloads from the Mac App Store are free.
Note during your trial that Aperture is hugely hardware demanding. Apple's published "System Requirements" are grossly unrealistic. Only the strongest hardware will trial Aperture at its best. CPU, GPU, RAM, i/o are all very important. With good hardware Aperture rocks but less good hardware will express less good performance.
If you get SBBOD ("Spinning BeachBalls Of Death") come back here and we will help diagnose why.