I believe mutton is old lamb, I mean when I say old, the lamb is killed at a later age making the meat a little tougher.
But they are both good, I personally buy goat meat and when you're in the shop, you cannot really tell what the butcher is selling you.
Are you making it the Jamaican way?
i have a recipe from www.carribeanfoodemporium.co.uk
it calls for goat, onions, spring onion, garlic, salt, black pepper, curry powder, hot peppers, oil, lime juice, boiling water, cocnut milk, butter, sugar and thyme.
Sounds right.
Try to marinade the goat meat after washing it in lime juice with the curry powder.
When cooking, the lamb produces a lot of water, so you may not need to add a lot more.
Some people like theirs runny, but I like mine thick and coating the meat.
Good Luck.