If you come on a 30 day visa exemption you can extend at immigration for 30 more days once. Then extend again but you will be denied and given 7 days for 1900 baht. You should have checked before leaving the country. Now you have used one of your land crossings inadvertently for this year.
Vientiane is arguably one of the top places to get your visas processed and they usually don’t give headaches to anyone.
Things do change though. Ask on this forum first before doing anything.