Its happened to a lot of people, human nature mistake. Just do whatever it takes to get a true sample from bottom of tank (where water will settle & where fuel pickup is located) . This will tell you how much you're gonna need to do. Or simplify it. Drain all the fuel, change ALL fuel filters & refill with fresh fuel.
I hope it's no water detected & just a good lesson learned. Embarrassing a little but hey, we've ALL had embarrassing screwups with boats.
'98 Tr20 Triton
'94 Merc 200Xri
92' ChampioN 201DCR Elite