How to get a straight line for pavers
Are you trying to lay to an edge or use the line for general alignmnet and to maintain a pattern repeat?
Pull it tight as you can.
No matter what it will not be where you want it to be eliminate the cutting the pavers considering the length of the edge.
Most contractors will run the pavers "wild" or beyond the planned edge and then snap a line and cut the pavers to fit the line (saw or split). You must cut the pavers to fit and then install the edging as soon as possible to eliminate the pavers from separating before vibrating. If you have curved edge, just get a gas powered saw and cut the pavers in place, install the edging, spread the top sand and vibrate to get the interlock and strength.