i have a big problem and i am very upset

i was working a large-ish house in creative mode. my work is about 60 by about 90 blocks and about 30-40 blocks tall. I have used redstone a little bit. so I was working and the lag was really really bad. then minecraft went unresponsive totally and crashed my computer. I get back in my game and start working again. again minecraft goes unresponsive. I have to get windows to force close it. I get back in my world after I figure out which one it was because it deleted my world name and said I hadn't been on it for a "long time". so get back into my world. by the way it is a flat world. so I get back into it. and what do I see? a load of chunks loaded with the non-flat type world biomes. I am really pissed because my game damn near crashed again. and I have tried to get a screenshot of the problem but my game crashed because your damned rain keeps killing my processor and because it spawns so damned much. so please help me!!!!!!!!!!!