It may not be possible to create fixed confidence interval that applied to all x values. Width of the confidence interval depends on the value of Xis. The CI band will be minimum around the x bar and the band width will increase as x increase/decrease from xbar.
The link below ans example of simple regression, shows how CI band in different xs.
If the CI band width is not varying much, then you could try average CI width or take the maximum CI band ( Max ( CI at xmin , CI at xmax) ),apply this to all observation.