Overprotective parent

How do I stop being an overprotective parent? I took my daughter to the playground and a little boy didn’t want to let my daughter slide. My husband came over to me and I asked him “why is she not going down the slide?” He replied “because there is a little boy not letting her.” So I just screamed and said “well tell him to get the f*** out the way!” Then my daughter walked over to all the other children and introduced herself. The children ignored her but still ended up playing with her in the end...when she got ignored it broke my heart...idk how I can emotionally handle her having to go through rejection, failure, hurt and pain. I don’t want to end up fighting preschoolers...