There are a number of things to unpack here.

First, your double was not “negative.” A negative double is a convention used by responder. Your double does not promise four hearts in standard bidding agreements. It suggests extra strength and no clear direction. Your second call should have been 2 hearts, not double. You have a textbook hand for that action: significant extras, four or more hearts, and longer clubs.

Second, you must not pass short of game. According to your rather specific agreement about partner’s jump in diamonds, you have 29-30 high card points between your two hands. You must, must, must, must be in a game, not a partscore.

Third, your stopper is not shaky, given the auction. How could opponents possibly be able to cash five spades? It is unlikely in the extreme for LHO to hold Kxx or Axx in spades, and in my book impossible to hold four to an honor; after all, they didn’t raise. I suppose you might find yourself guessing if RHO wins a small spade lead with a high honor and then continues with the J or ten; is your RHO the sort of player who would find that defense holding AKJT4 in spades? This is all assuming partner comes down without any help, like Jx(x).

Follow Hamman’s rule: if you have a choice of bids and one of them is 3NT, bid 3NT.

That’s still the case if you have KJxx in hearts instead of AQxx (where your double instead of 2H is justifiable, though I still think it’s an underbid). In order for 3NT to go down, you need partner to have something like Jx Axx KQJxxxx x (their 3D bid precludes having less), with clubs breaking badly. It’s still an OK contract across from partner’s worst possible hand. More likely, partner will have two or more clubs, a spade card, the ace of diamonds, or other cards that make 3NT a virtual laydown. Just bid the game.