@Barbora **********
totally will get in on a 45 day visa exempt entry and you can extend that ONE time for 30 more days at the immigration office for 1900baht
Unfortunately for you, if you do get the eVisa approved after you enter there is no way to use it INSIDE the country and as Lloyd stated you will need to exit/re-enter, by land or air to activate it and get the 60 days a tourist visa allows you.