screen got so big cant enter my sim number to unlock

my iphone4's screen got big all of a sudden by itself (did not do anything from the settings) now it is so big even when try to move from the corners i cant enter the numbers to unlock the sim. it touches zero in the middle and gets locked.

i turned it off and on took the simcard in and out. nothing works.

please let me know if there is anyone who faced the same problem and were able to solve it.

thanks

dilo