Take it easy is used to tell someone to relax and be a bit more carefree or to be gentle to oneself, so it makes sense here but it's more usual to say something like "Don't take it too hard" which focuses more on the fact that they could or do react negatively to things not going according to plan

Hi, Heidi! If you mean "relax" or "be patient", yes, "take it easy" is appropriate. Also, you should try "Calm down, everything is going to be ok!". Regards!