Help with 2D Platformer tutorial

Hello all, first post here.
I’ve been watching and using the fantastic tutorial on creating a 2D side scrolling platformer, and have found it to be quite beginner friendly and fun to use:

However, I have found a few issues in trying to progress beyond a certain point, and would greatly appreciate feedback as to what I’m doing wrong, and what I can do to successfully get further.
I have gotten to the point where I have created the single block tiles (though i did have difficulty when attempting to duplicate them. I found a different way around this, but it certainly wasn’t perfect).
Now, when attempting to slide the blocks and create the environment (whether in ‘front’ mode or ‘perspective’ mode, the blocks seem to show up in random locations. It’s very difficult to judge where they’re being placed, because unlike in the tutorial, I’m not getting the block itself sliding into view, but rather the movable arrows (please refer to the screenshot).Also, there is an automatic floor loaded into the template, which does not seem to be the case in the tutorial.