Is an 7.5 inch penis too big?

no,penis size average is from 6" to 7.5" inches.
Use lots of lube especially in the anal area,make sure she's relaxed and start off entering slowly.

no.

Um.maybe if she is not wet enough the friction could be painful, but actually I think that size is pretty average.

no you're fine, actually I think average girth is 5.5 inches and that's what would probably cause tearing so don't worry about it

Absolutely not. If she's healthy, the vaginal area should be very resistant to tearing, even with large insertions (like a fist). Just make sure you lube up every time, to make double sure she's comfortable.

Her anus can lacerate if you're not using lube. If you're putting it in her ass, use lots and lots of lube, and make sure you've prepared her first. (You should be able to slip in two fingers easily. Try a slow circular motion with one, then two fingers to spread her out.) You want it to slip in, not rasp in. More lube.

No-one ever died of a lube overdose.

It seems like you'd know that yourself since you're old enough. Wow did you say the anal area? Why are you concerned about that area since that wasn't designed for that purpose? You'd probably kill that!

it can tear a girl is she's a virgin, but that size is pretty normal