Nope, it's not possible.

When you already hit 300 good posts reported, you can only view and track your past 30 days reports to see the status is unhandled, good, or bad.

I see no problem if the forum will want to implement to withdraw reported post, but if you mistakenly reported your post e.g. duplicate or high quality post, the moderators will not likely to proceed your report and maybe it will stay in unhandled.