Transfer Text Box Data To Subform

This is a price check form so it doesnt need to be saved it just needs to display the part no info and quantities with price
If i enter a part no into a text box(PN1) on the main form it enters the data into a textbox(PN2) on a subform.
Im using a continuous form on the subform and the master/child link is the Part No text box.
is there a way to lock the first item to the first line and then be able to enter a second item to display on the next line.
I have made the size of the continuous form to one line in my subform but i am only able to enter one part no into the subform because when i setfocus to the PN1 textbox on the main form it clears the first line.

thanks