No problem.

Thinning epoxy will often lead to longer curing times. Compound that with the fact that you used 90 minute epoxy and it could take several days.

But something you can do to help it along is to keep it warm - I don't mean "Midwest Summer" warm, I mean hit it with a heat gun or hair drier. Maybe you can lay it in a secluded area and aim a hair drier at it and leave it overnight, or maybe even leave it for a day in direct sunlight.