Thank you for contacting us regarding your concerns.  Conservation plantings of wildflowers have gotten more popular, but can be a challenge if lawn and grass is close by the area.  Preparation of the area and adding a buffer zone is key to start.  University of Nebraska reccomends "If the planting is small, hand weeding or spot spraying with herbicides can be used to control plant diversity and eliminate weeds."  Here is the full article: https://lancaster.unl.edu/conservation-plantings

The first year or so is always the most challenging, even if you did good prep of the area, as annual weeds seem to be present.  Purdue has some guidelines about doing an evaluation and some recommendations as well: https://www.purdue.edu/fnr/extension/tips-evaluating-first-year-native-grass-forb-planting/

If this planting is part of a large planting, converting some acreage to habitat, you may want to contact your county extension agent.  They may be willing to come out and help with an evaluation and creating a plan with you.