So yaaah. Should I add a background? Either one of the beachy backgrounds or the backyard pool one, since it's for the summer thingy. And other suggestions would be appreciated too. <3

I would definitely add a background. It looks odd that your HA is ready to go to the beach and there is no beach, lol.

I always have a problem with adding backgrounds/not adding them when it comes to summer HAs. If you don't add a background, I would add some sort of beachy item behind it.

totally add a background, for sure :)