20 km Race instead of 11.25 km Long Run - Marathon Plan

Hello! I’m looking for some guidance here, either talk me into or out of it.

I’m starting the 18 week marathon training plan soon for a full marathon in September (my first).

There is a 20 km race that I would like to do that lands on week 3 of training which calls for a 11.25 km long run.

Am I crazy to do the 20 km race or should I stick to the 10 km which is also an option.

I did my first half marathon last September and have continued running 4-5 times a week averaging about 40 km a week and have done multiple 20 km+ runs in the past couple months. I know that I can handle the 20 km with my current base but I have some concerns about the following weeks in the 18 week plan. I just don’t want to mess up my training for my first full marathon…help!

Thank you for your feedback in advance, much appreciated!