I also had a borderline smear and HPV when I went for my last smear. I have been good and had a regular smear every year since I was 21, and this was my first ever abnormal result. I guess I am a lot older than you (45!)
As Holly said, HPV can lie dormant for ages and not do much. You also have to bear in mind that they don't bother to test for HPV unless the smear result shows abnormal cells, so it could have been there before but not tested for, so you would not have known.
Having high risk HPV does not mean that you will get cancer. The reason that the screening program takes an interest in it is that most cases of CC also have high risk HPV present, so it is quite reasonable that when they see cell changes plus HPV, they take it seriously and get rid of it. However, it is not the case that everyone who has HPV gets CC, far from it.
When you go for the colposcopy, they will do more diagnostic tests, to assess the level of any cell changes. It's quite fine, just like a slightly longer smear test. If the cell changes prove to be mild, they may well sort themselves out and you will probably be asked to return for another smear test in 6 months to make sure. If they are moderate or severe, you will be offered a LLETZ treatment to remove the offending cells.
As for trying for a baby, the LLETZ procedure can cause a slightly elevated risk of premature birth, but there are plenty of people out there who have had LLETZ and still gone on to have a family. It really should not affect your chances of that happening.
If all of this is making you really anxious, you could call the hospital where they will do your colposcopy and see if they can bring your appointment forwards a bit. They do get quite a few cancellations, so it might be possible, and at least you'd know what the deal is sooner rather than later.
I know it's hard, but deep breath, chances of it being anything serious really are very, very small.
** hugs **