a straight or upwards-pointing erection is certainly the most common type. i have seen porn where the guy's penis points down though. it's not unheard of, but i think it is quite unusual.
it occured to me that perhaps this could be an indication that your frenulum is too short and is pulling the penis at this angle. that's something worth checking out. i reckon it's something you will probably be worrying about until you get some reassurance anyway! so get a 2nd opinion.
if it turns out there is no problem with your penis, and this is just the way you are, then make the most of it! if you are confident in your sexual encounters then the girl is less likely to notice, and less likely to see it as an issue. and who knows, you could give a girl different sensations that she wouldnt get from other men! for example, doggy style or spooning could be really interesting
good luck, man!