I think your voice is really good. You've been told this by now in real life I imagine. I don't think you're singing too softly, I think your ukulele is just too loud in the mix. I would recommend turning down the ukulele's volume in the mix + compressing the vocals and boosting the vocal eq ranges until you can make the vocals pop more. Also there is this thing called vocal panning that helps vocals pop out of a mix more but I don't have the experience to help you with that. Go check out some of the other threads in the mixing forum, find the info you need to make vocals pop more, and thank the members in those threads whose advice you benefited from. Take care.
