Many of the larger models made recently are specified for nothing smaller than 'second radius'. Check your trackmat, and if it specifies first radius curves, and you intend to complete it, do so recognising that the loop with first radius curves will have to be restricted for some of your larger stock. Smaller locos and vehicles will run on it.
That said it is often worth trying to see what will run on first radius; if the track is laid very carefully on a level base, with no kinks in any of the joins, you may well find it is possible to get some stock labelled as 'second radius or larger' round these curves. But don't be surprised if some stock refuses and derails. Depending on how happy you are to tinker with the items that derail, you may be able to modify some so that they will go round first radius, but this will probably be at some cost to appearance.