Have a textbox value populate a certain range of cells only

I already have code to populate cells after multiple times of entering it in a userform. I also have other cells that are being occupied along the same row for another reason. What I am having trouble with is that I have a msgbox that shows up when the first row that is being populated reaches over 3 (or the 5 column). I want it to pop up only if the three has been reached and not count further down the row.

Can I make it so that the msg box does not count the cells later along the same row (column 6 and higher)?

Here is my current code:

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I have also attached the file in case that helps more.

I'm not sure I follow what you want, but maybe try something like this...

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