Ah, it's okay :) It's not too bad really. I was also a young mum (19 when DS was born) and I honestly never got any comments. I think it is really just a few people making mountains out of molehills.
When you first have the baby you will find it difficult to get out and about anyway just because of all the stuff you need to take with you, not to mention tiredness and recovering from the birth, you'll find that breastfeeding is just a part of that, so what you'll tend to find is that you'll overly plan at first and later it will get easier.
So for example, you'll probably look for nice easy trips to do first perhaps to somebody's house that you know, or to a baby group you've already been to (bumps and babies groups are great, there are also specific breastfeeding support groups or baby feeding cafes in some areas which you can start going to in the last weeks of pregnancy) or to a shop that you know has a feeding room, like John Lewis or Boots or Mothercare. Then once you're finding it a bit easier there, you might decide to go somewhere like a cafe that you know has little booths or enclosed tables for privacy, or somewhere that you can easily go back to the car to feed (if you or the person you're with drive). Soon you'll find that all you think about is whether there's going to be a place to sit down and you'll be away.
If you do want to use a breastfeeding cover you can, or you don't have to - one tip is to practice feeding in front of a mirror at first so you can see how much someone else would see (usually not much, if anything, at all.)
Also, if you decide to use ready made formula milk or express just for trips out you can do that if you feel more comfortable. It definitely doesn't have to be all or nothing. But it's definitely easier than you think to get to grips with feeding in public, and it will give you such freedom if you decide to, even only some of the time, otherwise you're always worrying about whether the bottle will last or whether you've brought enough etc.
Are your family supportive of breastfeeding, and do you have any friends with children yet?