Hey, this is my first review but hopefully I'll help you out a tad! 
Colors:First, let's talk color. This is a big problem with the entire level, but I'll start here. Color can take a really long time to get used to if you aren't super into art in general! When you start out creating, I suggest keeping colors to a minimum, as in try to only use different shades of one color. As you learn more, you'll figure out how to add contrast colors here and there. For example, let's look at the very first section of your level. Your background is set to blue. Now, you tried to have a contrast color by using green for the ground, but unfortunately, you didn't use the "Blending" tool! "Blending" is one of the best tools in the editor, it makes it so that your colors
blend in into the background. This tool should be used throughout this level to make certain contrasting colors less "in your face," if you know what I mean. The brown just does not work with the blue. Instead, you should try using different shades of blue, either darker or lighter, to compliment your background's color. If you are EVER having trouble with colors, there are many featured levels that have mastered colors. Don't be afraid to check them out and see how they made their colors compliment each other. Also, if you ever get confused with how someone got a color to look like that, they might have layered the object (AKA put an object with two different colors and blending on top of each other). Don't be afraid to copy a level (if it's available), and see exactly how they made their colors work! Just don't plagiarize...
Sync/Gameplay:Gameplay troubles a lot of newer creators, so don't worry so much about it. Gameplay is basically how well your level can be played and how well the placement of blocks and orbs also compliments the skill of a player. You had tried for an easy/medium demon. For a newer creator, I'd suggest starting out making easier levels, because the gameplay in demons can be difficult to master. People think demons mean hard gameplay, and yes the gameplay should be hard, but hard gameplay does not mean making the player feel overwhelmed or aggravated while playing the level. Demons are meant to be fun, yet difficult. Your level has some odd gameplay, where it makes the player not understand exactly what they should be doing. If you didn't do this originally, I recommend making a layout using the outline blocks and just basic orbs for your entire level before decorating. Then play the level start to finish with just the gameplay. Ask yourself: Did you ever feel stressed when reaching a certain point because you knew a jump was really difficult? Did the music help you in completing the level (we'll get here with sync in a second!)? Did you repeatedly die at parts and not necessarily have an answer for "why?"? Next let's touch on Sync. Your level needs to work on Sync, a lot! That's okay, it's an easy fix! In the top left hand corner is a handy button that lets you play the song in the editor. Use this frequently and match your jumps, portals, speed changes, and orbs to fit the song. I noticed that some parts did have this really well, like the beginning of that cube part around 00:50 seconds.
Decoration/Block Design:I think the best thing you can do is just look at some featured levels. Another tip I can give for this section is to find a geometry dash youtuber who gives creator tips and tricks or builds levels on videos. This helped me a lot and actually still helps me come up with fresh ideas or colors contrasting tips! If you want some youtuber suggestions, message me privately (not sure if I can shout out any channels on a review, so I'll play it safe lol). Decorations have their own tab, and going outside that tab for deco is really difficult, so as a starter I'd suggest just staying in that tab. Block design is really difficult at the start of your creating career. I'd say just learn how to make basic blocks and continuously add minor things to them, like a glow or decorations inside the blocks.
OVERALL:You do have a long way ahead of you, but I think if you learn your colors and gain block/decoration inspiration from other featured levels, you can make something that looks great!
I won't give a number score for this, because I don't want to deter you, but I'd say this level definitely
needs improvement. And that's okay! This is your first after all! Take your time and never stop creating.
