I know exactly how you feel.
In December (also just practice) I had the first 11, and the last shot was not off target, but knowing I was excited, I tried to make sure I didn't overthrow it with too much speed. In the process I rolled it just a shade slower and ended up on the Brooklyn side and left 2 pins. Not sure if it was the 9-10 or 3-6.
Like you... I have never had a 300 (been bowling for over 40 years, too), so it was a horrible disappointment to me. Then.... believe it or not...did the same thing again----including the slightly too slow last shot----9 days later.
Have not seen that side of 290 since, but.... the last couple of weeks I have thrown 4 games of 280 or better, and the shots that were not strikes in those games were NOT bad shots at all, so I feel good about those games. You will do the same too. You just need some time to get over the initial disappointment.
I know we both have a 300 coming for us soon. Hang in there!!!!