Hi- this appears to be a broccoli plant with a central flower stem that elongated and opened rather than forming a tight head. We see a side sprout (little head) as well. If the plant is doing well you may get a number of these side shoots (cut and remove the main stem with the flowers). Bolting is a common problem that can have multiple causes- often temperature stress, especially when young plants experience very cold temperatures. The plant should be a good deal larger. This plant family are "heavy feeders" so fertilize next time.

It's usually best to wait and plant broccoli in early to mid-April and cover with a row cover to protect it from insects and to increase the temperature around the plant a bit. You can start seeds in mid-July and plant a fall crop in early August.
Web page on broccoli- https://extension.umd.edu/hgic/topics/broccoli
Jon