I can give you a few tips on how to improve on this, I did it in varsity a while ago and got the highest marks for it.

First: use a ruler
Second: Use the corridor at the end of the passage and find the central point of the square.
Third: With the ruler in hand, every corner of the end passage from central point to corner is going to be your edge floor, wall and ceiling.

PS use your ruler throughout the corridor picture and you will get a great picture.

Ok, thanks! :D Yeah I didn't have a ruler at the time of the drawing heh, will definatly try it in the future ^.^

You wanna study to be a game designer. Oh interesting. You're gonna learn alot, very fast. If you want my help, just invite me and Ill teach you stuff I'm learning this year. On my FA page.

Awesome :D Yeah I have done 3D and digital stuff mostly, I have that stuff on my DA, but I need to learn to draw as well, so thats what Ive started doing! But will defiantly hit you up :)