Can I extend my tourist visa in Thailand without issues after multiple entries?

Hi together,

I have a question, i am from Germany and I entered to Thailand since the end of Oktober 3 times with this normal 30 days stamp. The first time I was 3 weeks in Thailand, after this 2 weeks in Vietnam, the second time I spent like 18 days in Thailand, and then I went to India for two weeks, I entered again to Thailand on the 6.1.2019, visa stamp till 4.2.2019 without problems, now and I stay in an ashram close to Chiang Mai and I like to extend my Visa for another 30 days, do you think that I will have any problems?? I think that I have to go to the immigration center, at what time I have to go?? Can I ask now or I have to do it at the end of my visa?? If I find a cheap flight now after my visa is ending, is this a risk, because they will not agrre to extend the visa?

Thanks and bests,

Kerstin