13w02b crash

i created a flat map and it said "out of memory" then i hit "back to title screen" and it crashed. it said that is was server but i was playing in singlplayer.
crash report:

---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 1/11/13 7:42 PM
Description: Exception in server tick loop

java.lang.OutOfMemoryError: Java heap space
	at java.util.HashMap.<init>(Unknown Source)
	at bq.<init>(SourceFile:12)
	at aaw.a(SourceFile:167)
	at aaw.a(SourceFile:89)
	at im.b(SourceFile:152)
	at im.a(SourceFile:179)
	at in.a(SourceFile:598)
	at net.minecraft.server.MinecraftServer.a(SourceFile:539)
	at bfd.q(SourceFile:113)
	at net.minecraft.server.MinecraftServer.run(SourceFile:614)
	at fy.run(SourceFile:850)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 13w02b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_05, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 8775240 bytes (8 MB) / 259522560 bytes (247 MB) up to 259522560 bytes (247 MB)
	JVM Flags: 1 total; -Xmx256M
	AABB Pool Size: 356 (19936 bytes; 0 MB) allocated, 131 (7336 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 60 (3360 bytes; 0 MB) allocated, 23 (1288 bytes; 0 MB) used
	Player Count: 1 / 8; [iq['howshotweb'/14, l='Plants vs Zombies', x=643.05, y=9.86, z=341.55]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.