Percentage uncertainty

Hello, I'm just wondering how ti calculate the percentage uncertainty of a 50cm3 burette with an uncertainty associated with the burette reading being 0.05cm3 and I did the titration 3 times so do I multiply by 3

No.

Each measurement has an associated uncertainty of ±0.05 cm³

To get the value for the titre you have to take two readings, so the uncertainty becomes ±0.1cm³

The percentage uncertainty is the 100 x (titre uncertainty)/(titre)

Each titration uncertainty is worked out in the same way, but different titres are not summative in terms of uncertainty.