Sounds like you are getting a 18...

Enter your vin here.

https://www.motorcraftservice.com/AsBuilt

Scroll down to the line that is labeled 720-03-01. Compare with the following

720-03-01 xxx5 54xx xxxx 36 Gallon Tank
720-03-01 xxx3 67xx xxxx 23 Gallon Tank
720-03-01 xxx3 D9xx xxxx 26 Gallon Tank