Writing : novice writer need help/constructive feedback.

In The Beginning

The day I found the opening was a lonely day, not unlike any other day.
It appeared in front of me as if a picture hanging in mid air. The landscape surrounding it was the normal view of my hometown, which consisted of green trees and blue skies. However what appeared in front of me was rectangular in shape and roughly the size of a man in length and diameter. Inside of this floating rectangle appeared a landscape so similar to that of its surroundings that the differences were almost imperceptible. Almost. Inside, the trees where taller by at least ten feet, suggesting a greater age than those around it, and the bark had a peculiar hue to it that reminded me of a solitary tree I had once seen on a camping trip with my father many years ago.
Also, being as it was around mid afternoon where I stood sweating under an oppressive sun, an immediate and startling contradiction blared out at me from within the man sized opening.

Wherever it was I was looking upon, it was now night.

  The only illumination coming from a full moon accompanied by a sky filled with stars of terrible size and dazzling radiance.
Approaching the rift, a slight tingle, close to that of static electricity, crept up my spine causing the hairs on my arm to stand erect.

I went home and went to bed.

The next morning the rift, as I was now calling it, was still there. I climbed through it and instantly felt…. nothing. I was standing in the same park under what appeared to be the same sky and sun. Looking around I realized some things were slightly off. There was a tree in front of me that was never there before, the buildings in the back of the park were dark blue rather than brown and the roads were black top rather than cement.
Now as I walked around and started to soak up the air in this new world I started to feel an atypical sensation, a sort of alieness. A foreign feeling permeated the surroundings and I began to feel saturated with it. I decided to walk to my house. The neighborhood was exactly the same except for a few small changes. A house on the corner that did not exist in my world, a stand of trees that should have been on the other side of the road all appeared in front of me ominous and threatening. As I got closer to my house a few of my neighbors were outside and they all waved and asked me how I was with huge smiles on their faces. That in its self was weird, none of my neighbors would ever talk to me let alone smile and wave. I wasn’t the most sociable of people and in fact I lacked even the most rudimentary of normal social skills. In school I was an outsider, the solitary boy who neither had friends nor wanted friends, suffice it to say, I was a jerk. Here in this new world however, people seemed to like me and I felt an almost suffocating expectation that I should respond back with a friendly gesture or greeting.
My house was on the corner. It was a red brick house with white front paneling and a large black front door. Everything appeared normal except the backyard was larger and there were a few trees that shouldn’t have been there. Suddenly I began to feel an overwhelming sense of nausea and almost fell to the ground. The blue sky became a sickening yellow and a voice in my head said run, get out of here you do not belong. The very molecules in my body felt penetrated by this alien air and I ran back to the window. The window back to my world was definitely smaller, at least a good two feet less in height and width. That was weird and deserved further attention but that would have to wait for it took every last bit of strength just to climb through the rift. I immediately collapsed on the soft grass of my own world.
Almost instantly the alien feeling dissipated and I began to breathe normally.

Morning.
I’m standing in front of the rift that leads to another world. I climbed through and noticed immediately that the weather is ten degrees colder here than in my world. As I turned and looked back into my own reality I watched with my own eyes as the window significantly decreased in size. At least another two feet in both dimensions maybe three. With a slight sense of urgency I realize that every time I climbed through the window it must shrink, close up a little. If the rate of closure remains the same I would give myself another two jaunts before the rift closes entirely. The sick alien feeling of unwelcome hit me again and I decided that I must suffer through this sickness. This trip must last longer.I needed to explore more and find out just what this place was all about.