I could do with some advice on my hair.

There's two things that bug me about it. The first is the sideburns and hairline around that area.
Is there anything I could do to make my hair more masculine? Really short hair doesn't look good because it shows how small my head is.
I squared off my sideburns to make them look more masculine, but I noticed that even young boys have more masculine sideburns than me. Mine don't stick to my face at all because my hair just doesn't grow there, so they look kinda silly.

There's also the way that my hair is just a straight line. I find that really feminine.
I want the sides to do that! Is that possible if my hair doesn't naturally do that?

if it was shorter itd prob do that

There's not much you can do if you want sideburns but don't have them naturally.  If you go on T, they'll grow in. Otherwise, you're stuck with what you've got.

if you went shorter on the sides and back (like a 2 guard on a shaver) it would help I think. as for the receeding hairline, it comes with time.

If you trim the hair around your ears more and outline the ear like the guy in your pic, it might give the illusion of longer sideburns.

The direcionality of yoru hair isn't the same as his either; notice that the sides of your hair are combed more downward than back toward the back of your head like his is...probably trained that way from years of combing and such. try brushing your hair back with a comb whenever it dries, to pull it away from your hairline...though it's not really that bad. Your hair is longer than his too it looks, especially in the back.

I'd suggest shorter hair on sides and back (and sideburns) and keep some length on top. Then it won't accentuate your head shape like an overall buzz would do. Having short hair close to your head around the sides and back ("puppy fur" as my kids call it ) does help masculinize many people's head shape. Also, having the neck cleaned up (blocked or tapered) instead of just ending in a straight hairline helps.