I want to be a better parent

So I'm a 21yo single mom with a 3yo boy, and I'm still struggling. This might be long but bear with me.My son has a roof over his head, a bed, clothes, food in his belly, I have a job. But I feel like I'm not present enough. I mean I am, besides work I'm almost always with him, he goes wherever I go.I hate to admit this, but I'm on my phone a lot. I'm aware of it but I dont know how to just stop. It's like my escape, so I don't have to actually think. And my son plays on his console a lot or watches TV or we watch TV together. I want to cut down on screen times for both of us, but I'm not sure how to start?I get so frustrated with my son. I try to stay calm but after asking him to do something 10 times in a calm voice and he just completely ignores me and I just end up yelling at him to listen to me. And I always feel bad about it because he always starts crying and wanting to hug and then I have to tell him I'm sorry and I shouldn't yell. Because now he yells when he's mad and I don't know how to get out of this cycle.And I'm very anti social, not so much by choice, it's just people make me really uncomfortable. Maybe it's some mild social anxiety but I'm not self diagnosing. And I worry its affecting my son because we never go out to socialize. We go to restaurants, playgrounds but keep to ourselves. He's not in daycare because family babysits him when I work. And I wanted to sign him up for sports this summer but just the thought of being around all those other parents made me back out of that.The fact that I had him when I was 17yo and I'm going to be a parent for the rest of my life scares the hell out of me. I feel like I'm never going to be enough. And I feel angry that I'm never going have the college experience I thought I would. And I'm angry that my son is not getting the childhood he deserves because I had him so young and that he's not growing up with a good father figure. I feel like I'm burdened with having to be everything for my son and that I'm not good enough.I'm worried that I'm going to resent my son one day or that he'll resent me. I love him to death though. He's a hard case and makes me so tired but I just want to be a better mom for him.And I guess I have a lot of other things going on in life and I've just been stressed out for years doing this parenting thing on my own. And I've gone to counselors but they just say that if I'm worried if I'm a good mom I'm probably a good mom. But I just don't feel like I am.So if anyone has any advice on any of that nonsense I posted, that'd be great. Thanks. via /r/Parenting http://bit.ly/2GPGrHj