is it normal? i am suspecting that gpu is defected (for other reasons) and this also makes me nerveous, i know if i double it, it makes the correct amount but why do i see it as 3506? is it ok?
That's completely normal. EVGA precision and MSI afterburner show the memory clock before it is doubled again due to the nature of GDDR5.
For example, my 660ti reads 3005mhz in afterburner when under load. That is exactly right, since GDDR5 doubles that 3005mhz to the 6ghz operational frequency.
The same is happening with your 770. 3506 x 2 = 7ghz. Totally normal stock speed.