Does my gas gauge work?

[merryprankster]

i put 7 gallons in, and the pump said it was full, i think, because it wouldnt pump any more gas, it would go for 1/2 a second, and then click stop. but when i turned the car on, the needle only went up a little past half way i think, maybe 3/4.
but i drove 160 miles or so, and now the needle is down to the second smallest dash mark. im nervous about driving anywhere cause i dont wanna get stranded.
any suggestions?