Need more exposure over a longer period of time. Alot of people talk about the 5 tones but then there's also you got to get used to the phonetic sounds as well. Some of those sounds are different or don't exist in English so we may not even be used to making a particular sound. When it comes for Thais understanding us there seems to be a certain level of importance with pronouncing correct vowel sounds (there's long and short variants) in addition to the tones. Just practice practice practice. Tones and phonics.
Thats strange, if you had the vaccine certificates they shouldve given you the 7 day. I just arrived today and they were following the new requirements