If it is unopened, you probably can take it back if you then buy Monokote as it is more expensive. The dealer should be happy with this.
If not, go ahead and use the Econokote, but brush a thinned coat of epoxy over the seams. Epoxy can be thinned with denatured alcohol, mek, acetone or lacquer thinner. What the fuel can’t reach, it can’t turn to goo!