To add onto what @randomperson42 noted with the idea of a grid, is that your UI - just based on your screenshot, not even actually playing the game - has no internal consistency to it, and fulfills few predefined expectations for a marble-rolling game.
First things first, one thing to note, is that usually users scan the screen in sort of a reversed N shape - more often than not, users start looking at the top left corner of the screen, scan downwards, scan back up and across to the top right corner, then down to the lower right corner. This sort of priority is important - important information should generally go closer to the top-left, with supplementary help links - which pretty much are last resorts - going on the bottom right. Primary actions usually go there in business apps, to, because you want the user to make sure they’ve entered everything before they hit OK.*
Starting with the title screen, you should really rethink it, in general. The biggest offender to me is, I don’t see a ‘start’ button or anything that would suggest where to start playing the game. This right there is going to be a massive turn off, and where I suspect you’ll see a lot of people just drop your app then and there. A clear starting point is the most important part of getting people to do something. Your settings button would be good to be close that, or somewhere in the lower right corner, along with the button for your ‘help how do I control the game?’ button. The specifics though are ultimately up to you.
The level select screen is irritating to the eye, for a different reason - even though your levels are arranged on the second ‘leg’ of the Reversed N, there’s also a general expectation that sequential information - like levels in a level-based game - progress downwards, from top to bottom, but vertically. This is influenced by how our language teaches us to read. If you were releasing exclusively in Japan, you might be able to get away with going from right to left, though the top to bottom priority would still matter, and even then I don’t doubt many a Japanese player might still find it a bit wonky. A purely vertical level select layout removes this ambiguity altogether, thus the recommendation for it.
In your gameplay screenshots, your Pause button would be better served in the top-right corner; from what I see your game is built for a mobile device, but there’s still the old expectations of affordance granted us by the humble console controller. Generally, our left hand is busy holding the device steady; our right hand is generally expected to be doing more complex things, like consciously hitting buttons. A right-top mounted pause button is easy for a player to reach, and follows expectations established by those that have gone before us. There’s also the slight fact that, as more people are right-handed than left-handed (I’m a lefty), it will be easier for a larger amount of your audience to pause the game that way.
I haven’t tried a playthrough of the game just yet. When I get a chance, I’ll take a look and see if I can give you some even more in-depth feedback. For right now, though, your GUI doesn’t encourage me to play the game; try improving that, as @randomperson42 suggested.
*: JRPGs are another example of primary actions on the bottom right, due to how previous works have implemented their UI. While the ‘Backwards N’ rule is a useful rule of thumb, it must always be tempered by knowing the interface expectations of the genre you’re working on.
Thanks in Advance!