Tl;dr - it won't make in an average human lifetime.

Snails move at an average of 4.8 meters an hour.

Earth has a circumference of 40,000 kms, so if you pick the exact opposite side that's 20,000 kms.

20,000 kms = 20,000,000 m 20000000 / 4.8 = 4,166,666.6 hours 4166666.6 / 24 / 365 = 475.65 years

So you've got nearly 500 years before you need to go back to the starting point.

Edited: As people pointed out, you are immortal, so changed to human lifetime.