He is a 3 month old Kenyan sand boa in a 10 gallon tank, placed on a tall drawer in my room. He is my first snake and I feel so guilty for allowing this to happen. He has possibly been lost for almost a week now (I held him last Friday. Was going to feed him Monday but couldn't find him. My mom told me to stop bothering him since he was also nearing his shed so I decided to not interact with him for 2 days. He wasn't in his tank at all after that). I apologize for any poor formatting as I am doing this on a phone and I'm really upset.
[This is a link to an Imgur post to the tank set-up because I don't know how to use this site on mobile] http://imgur.com/a/HYQcBff
I recreated what his tank looked like since I've made a mess trying to look for him. The aspen is definitely not that low but I do admit it was around an inch and a half (because I was told they didn't need much bedding) but I learned better and planned to increase his bedding once I got more aspen (which I did but now he's gone). The water bowl is in front of the fake plant. And yes, I was an idiot, thinking that I didn't need to weigh down the lid since "he's a baby" and "he's so low, he won't reach the lid."
I deserve being called out for my mistakes here but I want to firstly know how he escaped. Was the fake cactus too tall? It was pretty light so it can fall down easily (I would lean it towards the glass so it didn't fall). I see no other way for him to have escaped other than that cactus but then where did he go??? His tank takes up most of the space so he should've fell down on the ground and gotten very hurt, right? My floor is carpet so I don't know if he would've died or not. But I did check everywhere near the drawer, including inside, and did not see him. I have no idea where he could've gone or if he's even alive, especially since it could've been days since he escaped.

I apologize so much for not being able to prevent this. I have made a big mistake as a first-time owner. My mom says he's dead, which he likely is, but I just want to find him so I at least know what happened. I also live in an apartment so it would not be good to have a loose snake. I don't know where to start so I'm asking here. I'm sure I have done many things wrong and so I'm fine with any sort of criticism along with answers.