This is too tight.
'Stretto' — 'STRET-to'. Double 't', and stress on first syllable. Don't soften it.
When something doesn't fit because it's too tight. Clear feedback that helps the assistant find the right size or an alternative.
'Troppo' (too much/too) + adjective is the Italian pattern for expressing excess. 'Stretto' = tight/narrow. Opposites: 'largo' (wide/loose), 'corto' (short), 'lungo' (long).
È troppo largo.
It's too loose/wide.
Opposite fit problem
È un po' stretto in vita.
It's a bit tight at the waist.
Specifying the body area
Non mi entra.
It doesn't fit me / I can't get into it.
More informal — something that truly doesn't go on
Italian tailoring has precise vocabulary for fit issues. A knowledgeable Italian shop assistant will diagnose a fit problem with accuracy and suggest both size adjustments and alternative cuts — this is genuine expertise, not just a sales pitch.