Possible Parents for Sophia Watt

Sophia Watt's recently discovered obituary does not name her parents but does provide her date and place of birth;   March 26, 1782, in London, England.   Using this information I have uncovered a possible baptismal record for her.   There was a Sophia Watt baptized on March 31, 1782, at St. Leonard's Church, in Heston, Middlesex, which is part of London.  Her parents were William and Jane Watt.

I've also found a marriage record for a William Watt of Heston, Middlesex, bachelor, and a Jane Powis, widow, who married in St. Martin, Dorking, on June 19, 1780.

Powis could either be Jane's birth name or the name from her first marriage.  There is a marriage record for a Jane Bond marrying a John Powis at St. Marylebone on September 10, 1778.  There is also a record of a William Watt, Gardener, and his wife Jean Bond having a son named James on March 26, 1786, in St. Andrews.  A William Watt Sr. was one of the witnesses.  Could this William Watt and Jean Bond be the William Watt and Jane Powis who are Sophia's parents? 

Here is a death record for a William Watt, from St. Andrews and St. Leonards parish.

William Watt Gardner to St Mary's College St. Andrews died 27th of April 1800.

And here's another one, from the same parish, three years later:

William Watt, Gardner to the New College died here 6th of May 1803. 

Here is an obituary for a William Watt, gardener of St. Andrews, who died a few years before either one of these.  It is written almost 40 years later;  possibly the death date is mistaken?  It seems a stretch that there were three William Watts who gardened for St. Andrews University at the same time.   This is taken from The Gardener's Magazine and Registry of Rural and Domestic Improvement, Vol. 15, 1839.  If this is Sophia Watt's line of descent, I'm guessing it would be her grandfather, not her father.