68 is a good mark.
Tigger is not being rude, they are being straightforward. They are right insofar as you chose not to go for mitigation. If you thought you needed the time, then maybe you should have taken it.
With that said, 68 is a good mark and there is no point in you beating yourself up here. It is unusual to get a grade shifted unless you can prove an administrative error. It seems like your grade was affected by the dyslexia, but by how much is hard to gauge precisely. Given you were so close to a first, I don't think it impacted too much, but we'd need a breakdown of the rubric and your marks in relation to it to know for sure.
There isn't too much you can do. You could try the exam office or student support but it is unlikely anything will change.