It appears to be an Hydrangea macrophylla variety. These are often sold as houseplants and are only short term 'visitors', but actually they do much better outside, in a spot with soil that doesn't dry out frequently, in part shade or full sun (if the soil is kept moist), though they do get rather large planted in the ground, info here https://www.rhs.org.uk/advice/profile?PID=122. What's odd about your plant is the lack of colour in the petals - there's a hint of blue, but the individual flowers don't seem to want to colour up and open properly. If you repotted it (hopefully into something with drainage holes at the bottom) and used potting soil that was alkaline, that would affect the colour of the flowers, but I'd expect to see a lilacy pink colour rather than blue and colourless. If you can keep the plant going till next year by planting outdoors, it may produce better flowers, though perhaps this is a variety I've not seen before, with greenish/blue flowers instead (was there a varietal name on any tag?) - the flowers it has now will fade and die back anyway, but the foliage looks quite healthy.
