307 indicators ?????

friends mrb, i am a new member of gökhan, my car will be a question 2005 1.4 HDI 307 yesterday I bought 20 pounds of fuel, the needle was on the last bar, 20 yesterday I made an average of 20km this morning, but the needle was on the fuel gauge, it was half the time it had been before, it was past when I stopped and started again Why did not I try again, can you cause any other problems ???

the float can become stupid because you use fuel low