Suidjon

Thanks all for your comments! I gonna buy a extension to avoid all risks 

May I go to airport immigration and getting fined of 2 days a thb 500 and leave the country  then? ( cheaper than extension of 30 days)

Yes it is a 30 days visa exemption

Arrived at Suvarnabumi in Bangkok

I arrived on 14 March 2019 and got a permission to stay just till 12.4.2019?!?! 

(Why not until 14.4.2019?)

The problem is that I will leave the country on 14.4.2019 due to my booked flight

Now it looks like I gonna get a 2 days overstay fine?

Or what could I do?

Thanks for your advices