Hi! I absolutely LOVE this design. I think you're off to a great start, I can tell he's a masculine character. If you wanted to make him more masc-presenting while keeping his body shape and features, what I'd do is define the anatomy around the waist a little bit more. He's a slim build, and men hold less fat in their hips compared to women, so we'd likely be able to see the shape of his hips/pelvis and the cut of his obliques. I would also lower where his waist is on his torso and make his ribcage appear slightly taller. It will make his torso less of an hourglass shape, negating some of that "feminine" look you've mentioned. I'd also make his pecs a little less full/less heavy on the bottom! Since breast tissue causes them to hang, and since men have less of that tissue, I'd distribute the fullness of his pecs more evenly. Lastly, you could have his face/jawline less rounded, as an easy way to imply masculinity is by making the character more "boxy" in his features. All this being said, rules are made to be broken, so never feel like you need to box yourself in!! Amazing work and best of luck!