A couple of things might help:
Do you have Snap to Grid turned on? You can find it under the Grid menu:
Also, here's a tip for aligning the sides of two objects:
1. Tap to select your first object; then tap and hold on the center handle of the side you want to align the second object to:
2. Continue to hold, and use another finger to tap the second object. The second object then aligns to the first:
Let us know if this doesn't work for you. Thanks for posting!