this plant is growing where beebalm was last year, but it looks like a weed. is it beebalm?

It looks like bee balm. If it has a square stem and aromatic leaves when you squish them that should confirm it.

And if its growing where the Bee Balm was last year, that's a good indication its Bee Balm. It does look like Bee Balm (mine are at about the same growth stage).

thanks for your replies. Does Bee Balm spread indefinitely? it seems to be really expanding its footprint. will that continue until it takes over the whole garden bed? if so, how do you control its expansion?

It can be a vigorous grower given the right conditions (full sun), easily controlled by pulling it out, transplanting it to another location or giving it to neighbors!

It likes moisture too, and yes where it is happy it can take over a whole bed if you let it, and get mixed in with other adjacent plants. I've contained it either by chopping off bits at the edges to keep a buffer zone, or growing it in a bottomless tub so that it can't spread beyond the confines of the tub/bucket (my grandfather's remedy for controlling mints), and in one case moving it to the edge of a pond where it can spread as far as it wants and it really loves it there.