You did not post an image of your blocks Jules, that would help give you specific advice. The first message goes out ok. Great. Now why do not the final two messages?
Either this is a timing issue; you request sending messges 2 and 3 before 1 is sent
or
one of the messages is longer than 160 characters (including spaces). There is a limit to the 'length' of a standard sms message.
You might fix a 'timing' issue by using a Clock.Timer to create a delay between messages. You could also use three buttons, each of which would send a message provided you wait between button touches.
Try some blocks. The problem is probably timing. When you get a solution, please post your blocks here Jule and / or show us what you attempted..
Regards,
Steve