Make sure to use the grid system. When you're placing items in grid mode, make sure all items placed are in the same grid size, or it would not be aligned well with others.
When you drag out the item you want to place from your inventory, depending on where it landed first, it could have its orientation offset to them. This causes some items to have very odd rotatio ticks. In this case, you can reset the orientation when you are holding on the surface you want your item to be, and have them properly positioned.
Tower Unite building system isn't very intuitive. It is possibly one of the worst ones I've used in a building game.
It's not just you. It's just really outdated and very user-unfriendly. The developers are aware of this and improvements are planned.
The main problem with the building system is that it requires you to hold buttons to just place an item.
Hold Q to open the up that tiny menu (which could be bigger to have more items listed) while you search for the item, and then drag & hold the item until you find the perfect place for you to place them.
Usually, in most of the building games, it only requires the player to either have the item selected in their hotbar, or just simply click the item once to hold them so we can place it easily.
The good news is that improvements are coming. If I remember correctly, mac is aware of the problems I listed above.
The bad news is that it is not coming with the upcoming Portal Condo Tools update.
The improvements are overdue, and it is coming, but not anytime soon. In the meantime, you can wait for the next update to help you work more efficiently with a few new tools.