Having one testicle lower than another is fairly normal. I have seen many, many pairs of men's balls and this typically the case. Of course when a man is aroused and his penis is hard his balls tend to get tight and when this happens there is usually no visible difference in size - there just tight and hard as rocks. Of course once the guys shoots and his penis deflates the testicles become uneven again.

Regarding ejaculating too quickly, you need to work on control of your penis and try to start and stop while stroking. The idea is to try and prolong the jack off session prior to shooting.

Hope this helps.
Wendy