Feel like a failure

I feel like a failure sometimes - especially late at night or when I'm trying to flirt with a guy. Aside lack of confidence over the years, my big sister was pregnant at 14 and I've always been worried I'd screw up but over the years ive felt like I missed out on a lot and I have never actually been on a date or had a boyfriend, the girls at school use to bully me and put me down to the point where I'd hide away in classrooms to feel safe - at 25 I feel kind of like a lost cause especially lately when I'm trying to lose weight and gain the confidence to actually try and go out or do stuff with the guy I like and go he is probably sitting there talking to five other girls way more experienced and confident - it's not like I'm waiting til I get married (I'd probably keel over first lol) cause I seriously want this I just have this nerve in me that sets off and makes me feel like this.