Staying calm in chess, especiallly under pressure

Hello all, I`ve recently started playing in USCF tournaments and have been hovering somewhere between 1550 and 1650. I have a question, primarially for the higher rated tournament players on this site: what`s your method for staying calm during the game - controlling yourself, not just the pieces. A week ago I played a Swiss round-robin tournament, by round 3 I had 1.5 and I played a kid that had 2.0. I was clearly better than him and won the opening as white with a personal favorite, the max lange attack with 5. 0-0 Nf6 6. e5. It was rapid/normal (45/10) and I got a little overconfident, and made a speculative bishop sacrifice on f7 that didn`t result in any immidiate tactics, just drew the king towards the center. After about 5 moves (which he played perfectly according to stockfish) I hadn`t achieved anything though his king was still vulnerable - I started to panic a little. Two sets of minor pieces had been traded and I was down a minor piece to a pawn, with no clear continuing attack against the enemy king. Also, this was a little kid - which always throws you off a bit. The game continued and it was a tactical slugfest, but neither side gained a significant advantage. Because I was so un-calm, I missed some clear attacking lines and some tricky tactics (that would have worked according to stockfish). I lost the game and the tournament because of it. This isn`t how all my games go; most of my tournament games aren`t as spicy as the max lange (I tend to play Carls-Bremen English against players who are better than me, just because it throws off their opening preparation and I know it well), though I do like the KID (especially the Bronstien variation of the Saimich - queen for bishop pair and two pawns yes please) as black. But if I win the opening (I obsess over opening lines way more than most players at my level) I start to panic - I feel that I should win the game, and mess up the attack or miss some tactics. How do you guys control scenarios like this? Indeed, the hardest game to win is a won game. Tips for staying calm and in control? (and yes I know the title has 3 ls, idk how to change it)