You don't say which measurement is width. I assume the path is through, and confined by, the garden and as long as the garden width. If not, there is too much missing information.
However, the area of the garden is 11x15 = 165 ft², so what is the problem?
W x path-width < 360
path width < 360/W
if W is 15 ft, path-width < 24 ft (the length is only 11 ft)
if W is 11 ft, path-width < 32.7 ft (the length is only 15 ft)
You have more than enough.