The Wrens make the short trip to the Forest Town Arena on Saturday to test themselves against former boss Rudy Funk's Evo-Stik League new boys AFC Mansfield, who hit Midland League Kirby Muxloe for six in the last round.
And they follow that up on Monday by welcoming Clipstone to the Tomlin Personnel Stadium.
Marvin admitted that the defeat at Ashby was hardly the best preparation for a coming massive weekend, indeed of the eight halves of football that Rainworth have played since the start of the season, the first half at Ashby was their poorest.
But he said: "The lads went out for the second half, tried to do the right things, and looked a much better side, but despite creating a few chances they couldn't overturn Ashby's two first half goals.
"In every game so far we have started poorly," he continued, "so maybe we need to tweak our preparations so that we are out of the blocks from the start - we can't keep chasing every game as we have had to do so far this season.
"I hope we can leave that first half performance behind us as we go into this weekend."
The Wrens' boss readily admits his side will start as underdogs at AFC Mansfield on Saturday. Last season the two clubs were in the same league and both matches were drawn, but the Bulls were promoted to the Evo-Stik League while Rainworth took a voluntary step down, meaning there is now a two division difference between the clubs.
"We know it will be a really tough test for us," he said, "but we will go out there in a positive frame of mind and enjoy the occasion.
"As last week we will have a number of players missing, but that gives an opportunity to those who come in to keep their shirts if they perform well. We've been working hard to bring in a few new players and are always seeking to improve our squad."
Looking forward to Monday's visit by Clipstone, Marvin continued: "They are now unbeaten in three, they have achieved their first league win in well over a year, and recorded a magnificent FA Cup replay win at Barton Town, so they will arrive on a high, and we've got to go out and match that, stay positive, and see who comes out on top of what promises to be a very good game."