Here is your program with some comments inside the block diagram. Try to keep the wires straight as much as possible, makes it easier to read. Learn about execution flow and data dependency. Use the Error wires to dictate how the execution will flow. All functions will only be executed when all of its inputs are present. By using Error In/Out, the 2nd function will only run when it receives the Error Out from the 1st function. This dictates that the 1st function will execute and finish before the 2nd function starts. With GPIB, you should only send one command string at a time. You need to send a read command before you can read. Usually the read command is something like "Read?". Check your instrument manual for its read command.
Learn how to program without using sequence structures. You could create your entire code without them by using the Error In and Error Out wires to dictate the execution sequence.
