Unable to Avoid Losing a Won Game

I'm an average chess player. Sometimes I attend tournaments and I have multiple loses against my level or better players. Commonly I end up playing OK at beginning and middle game, but the end is different. I think I can't seem to focus on board at late moments. Slight talk between refs or players making immediate analysis of their finished games right there affects my moves.

Today, a few players were watching my game. I was ahead by a pawn. Ref warned nearby players who were watching my game. Those players didn't make any noise but ref thought it was necessary to warn those anyway. Interestingly after that warning, I didn't calculate my move correctly and made a silly mistake. Trying to avoid continued checks, I was looking for a safe spot my king and the spot I placed my king was dead end for me. Locked by a pawn and queen, there was no escape route for my king and checkmate happened immediately.

After that game, I wanted to beat ref. Of course, it is my mistake but I feel like I should keep them responsible at least 1% percent.

On a side note, refs are visiting tables during middle game and take some notes regarding move numbers and clock. This is not a good idea because it breaks focus on game. Maybe those moments are not important for other players.

How can I ignore such moments and silly mistakes?