Summons for cannabis driving

In February I was given a roadside test for drugs and drink at a random checkpoint. Cocaine came up in the saliva test but I had not taken any but when I went to the station and got the blood test to show I had not taken it a few months later it came back with canabis. I did smoke the night before quite a bit and I was a regular smoker at the time but canabis came up in the blood test at 2.7ug yet I had not smoked that day and was in no way impaired I did not even think it would show up tbh and I said to the guards at the time that I smoked the days prior after they did the saliva test but it had almost been 24hrs since I last smoked. I have since actually quit smoking but I got severed with a summons today in November over 9 months later. I'm a recent graduate and am moving abroad in the next few months I was wondering if I anyone with experience in this sort of thing or type of law that could offer some advice and also let me know how this could effect my application for visas and jobs in the future to Australia and the USA etc. any help or advice would be greatly appreciated I was in a bit of a panic today when I was given the summons as I did not expect it and also don't really know what to do about it now.