Adding Border to a Cluster Stitch

[MagnusJ98]

I'm having problems adding a border to my cluster stitch swatch. Please help. 

[bgs]

What exactly is the problem?  A photo might help.  Borders can be problematic especially working along the sides.  Are you following a pattern or are you trying to select a border?

https://hearthookhome.com/how-to-add-a-border-in-crochet/

[Granny Square]

Agree with Bgs; for me, adding a border to the sides is mostly about picking a scheme of which loop-choice to use along the sides, and then being consistent and at the same time, if necessary, tweaking covertly to keep the fabric flat.

Another issue - if you want a 1 row plain SC or DC border, that's pretty easy and you just have to worry about turning the corner based on the stitch you are using (sc, ch1, sc, for sc;  2dc, ch1, 2dc turns a crisp looking corner).  If you want a more complex border, it gets more difficult really fast - you need to take the stitch repeat into account, to ensure it is going to fit, and not look wonky once you get to a corner.