The main worry for me would be lubrication of the metering fuel pump
. The lubricity of ULSD is already rather marginal, and the addition of several percent of gasoline will drop it a lot more, far more that the proportional content.
The more modern your engine
, the more likely is a problem, as new engines run at higher fuel pump
There are 3 plans I can see :
1) Stick a few bottles of diesel lubricity additive in, and use the fuel.
2) Demand that they remove the fuel, and replace it with uncontaminated fuel.
3) Request that the marina warranty your fuel pump for the next few years. Unlikely to happen, I know.
What would I do? If the mistake is the marina's, (2), I think. If mine, (1).