You don't need a long d*** for sure. Just enough to reach the small bump inside of her (usually 2 inches in) and that's fine.

If it ends up being deeper, a finger can help.

If you're not happy with the diameter, then you can ask girls to learn kegel. Still is the exercise for choice. And for men too.

It's still a fun experience if that's the aim. If the aim is ejaculation for both parties at the same time, I suggest you forget that. That's another rarity.