First of all, are you using Scotland's People or some other web site as your information source?
See
https://www.rootschat.com/forum/index.php?topic=714261.0SP has baptisms of five children of Robert Main and Janet Park: Lisabeth 1752, James 1754, Margaret 1755, Janet 1758, David 1767. It also has two marriages of Robert Mains in Dumfries-shire, one in 1751 and one in 1756, but neither gives the name of the bride! It would be not unreasonable to suppose that the one in 1751 is with Janet Park, but the original record doesn't say so.
SP also has a baptism of Jannet Park to John Park and Jannet Hislop in Eskdalemuir in 1731.
Again, it's not impossible that Janet Park, born 1731, is the one who married Robert Main in 1751. It is unusual, but not unheard of, for a woman to marry at 19 or 20.
But it isn't safe to make the assumption that it is the same one. The further back you go, the more gaps there are in the surviving records, and the greater the likelihood that the baptism or marriage you are looking for has simply not survived.
SP has no records of marriages between a Park and a Hislop. Unless they owned land, or left a will, the chances of finding out reliably who Janet Park's parents were, and anything more about them, are very close to zero.