The contamination can be coming from 3 places in your case: the spores/LC (since you said injecting, but it seems like you’re using spores), the spawn, or the environment during inoculation. If you followed sterile tek like you said, the most likely culprit 99% of the time is the syringe. You can get into agar for about $20 following PGT’s tek on YouTube if you want to increase your success rate, but it’s all about the failure rates you are willing to tolerate. The contamination rate using spore syringes is entirely luck, based on how sterile the supplier was. When you test syringes on agar you will realize some syringes grow nothing but bacteria, some never germinate, and some grow clean mycelium every time.