Hello alyssa___chouinard
It appears you are having some difficulty with a group chat that you were invited to.
Send a group message on your iPhone, iPad, or iPod touch - Apple Support
Try forcing the Messages app to quit and then reopen and see if the chat appears.
How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support
As a last resort, if the group contains any non-iPhone users, it's an SMS message which is 100% the purview of the carrier. In that case, you can try deleting the thread and then adding back a new group thread that includes all of the same people.
About iMessage and SMS/MMS - Apple Support
Cheers.