Partner (not you) opens a mini 1NT, 10-13 HCP, 5CM or 6Cm allowed, or any 5422 except both majors (but if partner has a 5-card major it will be weaker than a normal opening bid)
Your 2♣ asks for a 5-card major. It did not imply any high cards, so partner would always have passed over 2NT.
2NT was any 2-suiter
You bid 3NT to stop LHO giving RHO any help with the opening lead
Lead

Help

1NT P 2♣ 2NT
P 3♣ 3NT 4♥
P P x P
P 4♠ x all pass