The /r/ is a tap, or flip, of the tip of the tongue against the palatal ridge behind the upper front teeth. It’s not a curled-tongue back R as used in American English, which sounds like the final R in words like “teacherrrr” or “fatherrr.” Therefore, if that’s the sound we associate with the letter “r”, then the Gaelic r doesn’t sound like an R to us at all.
You are probably asking because in other situations toigh and toil seem to be interchangeable, as discussed here for example for 'S toigh leam X / 'S toil leam X. This means 'X is agreeable to me', hence 'I like X'. Toigh is the original and it confused with toil when it is followed by an l, and now both are accepted.
But this is different. This is using the word toil 'wish' to say mas e do thoil e 'if it is your wish' hence 'please'. So this usage has nothing to do with toigh and there is no risk of confusion as it is not followed by an l. So it is - and can only be - mas e do thoil e. Note however, that it was not very common to use anything for 'please'. It only became common when English speakers wanted a translation for please, and the phrase was virtually invented for the purpose.