I'm in that exact spot of just overweight where clothes entirely conceal it, but it's very obvious if I take them off. It hasn't bothered me enough to do some exersise and get rid of the excess, but it's always there in the back of my mind. Very annoying.
Not lasting long enough is a pretty common concern, to the point where a lot of guys I know try to carry on after they've.. finished.. and it just makes the girl they're with feel awkward. Peronally, I learnt a few tricks that let the guy last longer (no I'm not going to go into that here, go talk to Google) so I don't get nervous about it per sec... only embarased when the tricks don't work.
By the way, some advice with the scars; there are some people who value them as an attractive feature instead of just not being bothered about them (some people like me, for instance). Be careful with these people, I've heard stories go both ways where one partner has a fetish for the other's insecurity: sometimes the insecure partner feels fantastic that the thing they're nervous about is actually liked, sometimes it gets worse because it's always brought out. Like me with scars, I'd always find myself tracing them, which could make the problem worse.